What's wrong with this system?

I have had my current and first real system for about a year. The problem is that a lot of music (especially classical) sounds blah and uninvolving, and I don't think I'm hearing nearly enough details as I should. Here are the components:

-Cambridge Audio D300SE CD player
-NAD C320BEE integrated amp
-Monitor Audio Silver S6 speakers
-Audioquest Diamondback interconnects between the CD player and the amp
-Van Den Hul 'The Clearwater' speaker cable (two 8' runs)

I should mention that my listening area is about 15' x 15' with an 8' ceiling. I would like to 'fix' the system soon, and could spend about $1500 (but wouldn't complain if I didn't have to spend that much, of course!). On a side note, I have been told that tubes would not work with my speakers because the combination would be too warm. Is this true?

Thank you very much for any suggestions you can give me-
Who said it would be too warm, your ears? If not, then it ain't true ;)

I have a set of Diamondback and know the sound. I would suggest upgrading them.

Cheers :)
I would upgrade your cdp. For $1500 new or used, you will be able to get yourself a cdp that will deliver the goods. Caution! Danger will Robinson, this may lead to an upgrade of additional components down the audio highway. The nature of the audiopool beast in us. peace, warren
Cambridge CD player while decent in the bargain class is not up to the NAD or Monitor speakers. The Cambridge 500 is far better or a better match would be a used Audio Refinement. Try Signal Cable for interconnects. Good luck.

Could you share with us setup details of your system / room, i.e. accoustic treatment, vibration tweaks, speaker positioning, rack? floor carpeting...
Take a look at Dirtyragamuffin system and you'll see wall treatment (auralex),power tweaks in other words I'd suggest to check the complete setup to really open the capabilities of your current gear. This could provide a solid foundation to any future upgrade you invest on.
In my book setup is a high priority
I have to agree with Celtic66, I think the Audio Refinement would be an excellent choice. I've seen them used for under 600. That should give you more of the detail and realism that you might be looking for. If it were my system, I wouldn't worry as much about the cables right now. You and I are kind of in the similar stage, and I think your money would be more well spent on amplifier and/or cd player at this point.
Some good advice already. As far as the system goes, I'd agree with Warren: start with the source. I don't think you need to drop the entire $1500 there. As he suggests, you will find that upgrading a single component may lead to revealing faults elsewhere. I would think you can find some source bliss in the $1k range that would still be a significant improvement on your Cambridgge and put aside the balance for the next upgrade. Also, as has been suggested, FIRST look at the room as the source of your problems. A room can make or break even the best of systems, no doubt about it!

Keep the equipment the same for now, and read up and learn about room acoustics, proper system set up techniques and acoustical treatments (which don't always have to be ugly wall panels). Experiment with placement of speakers to try and understand their interaction with the room. Your system is not bad, it probably is just interacting poorly with your room.
I'll second the room acoustics. Here is a resource page on our website. It has lots of books and web articles that can help you. It even has a free room simulator. Your 15 x 15 dimensions are difficult, and you will likely want to experiment with an assymetrical placement that can at least reduce the modal problems at the listening position to some degree--or over time you may decide to correct for the modal issues with a paramtric eq such as the Rives PARC.

Acoustics Resource Page
I third the room issue. Before making any equipment changes you need to do something about ypour 15X15X8 room.
"Danger, Will Robinson!" is right!

In 1995 when I could first afford it, I went out and bought an NAD CD player and receiver with NHT satellites and sub.

Although I'd never heard a really good system, I thought the same thing as you, "a lot of music...sounds blah and uninvolving". Not even close to what I'd imagined.

Room acoustics and speaker placement might help you, but be wary that you may just be beginning your descent down that steep, slippery and expensive path to what we call audiophile-upgrade-hell!
I'd suggest replacing the NAD int. amp with perhaps a McCormack DNA 0.5 amp (and an inexpensive preamp) or perhaps an Audio Refinement Complete int. amp.

Next, I would look at proper line conditioning, installing dedicated circuits/lines, etc..

More than likely, a part of your problem is that all digital cd players generate a bi-directional digital noise that gets back into the wall and then into your int. amp. This digital noise can certainly make listening less pleasant.

If you should consider any line conditioners, make certain that they provide bi-directional filtering.

You might also try moving your speakers around for best placement/sonics. Somewhere in this placement process is a magical spot that will minimize some to many of the room acoustic deficiencies. Be patient as this can take weeks or months.

I suggest dedicated lines first and then see what you have, wait at least a month before you change anything after installing the new lines.

A tube amp can be very neutral. My Audio Note Soro is the most neutral amp I have ever owned and it is superb. I recommend them to everyone who has an interest in tubes. It has an excellent phono section to boot.

If you do not buy tubes I would keep the NAD and change something else as I have read way too many raves about that amp to get rid of it...
Two more cents, as if you needed them... you will be happier with a better player. A Music Hall CD-25 might do it for you. I liked mine a lot, and even more for what it cost. Later on I sold it for a Shanling CD-S100 Mk II, which is in another league for not another league's worth of money. Unfortunately it's not for sale in the States AFAIK. But my point is that for under a grand you can get a player that will give you more of everything than your Cambridge.

I absolutely agree that the source is where to start upgrading.
Dedicated lines and power conditioning are certainly ways to go, (on down the longer audio highway) but considering your system, you'll get more bang for the buck with a cdp upgrade. As Marco stated, you certainly don't have to use the entire $1500 to move up to a much higher source level than you presently have. Buy a pair of Golden Cardas ref ICs, or something of that quality. You'll be on your way.
Purchase upgrades that you will use for now and forever..Fundamental upgrade that you can use under a Nad a Krell or an SET..An upgrade to a preamp speaker or CD..Audiopoints or Sistrum will give you a remarkable degree of improvement in every way..It will be the first time that you ever truly heard your system and will keep on ticking with your next system. These products will also improve the overall efficencey of your system..Yes I am a dealer..Eight years prior I was...well only a user..Tom
Thanks to all for the valuable input. I think before I do anything I'm going to get an SPL meter and a test cd and see what's going on with my room, as some of you have suggested. Here are more details about the setup of the system. I live in a studio apartment (for now), and the 15x15 area I mentioned is actually only about half the room--the one where my system resides. I am not using any isolation equipment, and the amp and cd player each has its own shelf on a wooden cart-type thing, which will also be replaced soon. The components are plugged into a power strip from Accoustic Research (about $40), using the stock power cords. The speakers are 5' 4" apart and two feet away from the back wall. The left speaker is 3' 2" away from a side wall and 3' 8" away from a corner. There is about five feet of open space to the right of the right speaker. I know this is not ideal, but the speakers can't be moved around too much (the whole system can't be moved much). I think the corner is causing some boominess in the bass, and even at two feet off the wall the bass is overemphasized at times. Plugging the bottom ports on the speakers (there are two in the rear, top and bottom) tames the bass a bit, but results in an overall 'constricting' of the sound, which I don't like much. What I have tried to do is pull the speakers as far away from the wall as the room will allow so I don't have to plug the bass ports. The speakers are toed in about an inch. I have experimented with pulling them out very far away from the wall, not toeing them in, etc. They are spiked into the carpet, which is a medium pile. Is anyone familiar with these speakers? Maybe they are just not happy in my apartment. Either way, I do realize now that the Cambridge Audio is a weak point, and I am not impressed with the build quality of either the CA or the NAD (coarse, unbalanced volume control). Regarding replacement of the CD player, how would an Arcam like the CD62 or CD73 do? Thanks for all the suggestions, much appreciated.
You might try to deal with that left-side corner. A cheap way to see what effect treatment might have is to buy a standard bag of pink fiberglass insulation ( 4 feet tall ) and stand it in the corner. This is the simplest bass trap I know. Keep the receipt so you can take the bag back, since WAF is on the negative side. Even I hate the way mine looks, but that's not why I'm keeping it.
I have to agree with the input that the greatest issue is room acoustics. The speaker set up can make or break your system. Too much bass enhancement clouds your highs and midrange. This clearly seems to be the case here since mids and highs are the particular strongpoints of the Monitor Audio speakers. There's no shame in plugging the bass ports if it pleases your ears. Furthermore you could put some extra damping material(wool or BAF wadding)in the speaker cabinet. Make sure you don't block the BR port. Also, the 1:1,2 rule works miracles. If your speakers are 2 meters apart your ideal listening position is 2,4 meters from the speakers. You can then finetune the stereo imaging to your taste by rotating the speakers inwards or outwards. Upgrading to a new source will put more refinement in details and add some clarity but will most probably not lift the veil in your system. I have heard budget systems sound very open and unveiled eventhough the missed the microdetail that high end offers. Good Luck!