NO, it's not always necessary, whether it will be better is a question that cannot be answered in general though. It will critically depend on whether your cdp is a good match in electrical terms with your amp and, of course, the individual as well as relative quality of your cdp, amp AND the pre-amp you intend to use. I would avoid the direct connection if the volume control is in the digital domain, though (unless you go Wadia, phew, narrowly escaped stoning there).
Your consideration on going for first class cdp and amp now and, perhaps, adding a pre-amp later looks optimal to me. Remember you also save the immediate cost of one more IC and one more PC. And it's not only a consideration of cost, but also an interesting adventure in audiophilia, I would have thought (I am experimenting presently with a Ancient Audio Lektor V fed directly into Kharma Matrix MP 150)
I bet those sales reps all had the ideal pre-amp to sell to you, huh?
You will usually give up some convenience like no additional inputs, and most likely polarity control. Polarity can be resolved by inserting an inexpensive XO like dBX or Behringer. Both have individual polarity control for bass, mids, and highes, as well as Left and Right channels. I prefer the Behringer CX3410 because it also has a sub output. Most of the time this is where the polrity is out.
The Raysonic 168 and 228 have an outstanding balanced variable tube outs.
In some situations the direct connection of CDP to amp will give better resolution of fine details. Some consider this to be a more pure approach.
The preamp system will likely give better dynamic performance with more slam and impact.
Those are generalities which may not apply to every system.
Try it and see, if you get a pre you can always sell if you don't need it and it will be fun to learn the differences and pros/cons in YOUR system!
It simply comes down to preference. I use CD direct to amp for the simplicity, cost savings and great resolution. I may give up a bit of dynamic drive, but honestly I couldn't tell the difference when I stuck a pre-amp into the mix.
If you only need a single source system, try CD direct. It might save you a lot of money that you can save by not buying a pre-amp.
In my experience,with my equipment there has always been a loss of fidelity or musicality,if you please,with a direct connection between the source and amp.
My preamp is the heart of my system. An active preamp has a tremendous effect on the sound, IME. Proponents of passive preamps would obviously disagree. In your situation, you could use a direct connection and then, if you can borrow an active preamp from a dealer or a friend, compare your system's sound while using the preamp. Just keep in mind that different preamps have different effects on the system's sound.
I have owned a Mark levinson # 39 CD Player and currently own an ML-390S, I have used both through the ML-326 pre-amp
and directly to the Amplifier. One reason both CD players sound better through the pre-amp is the ML-326S NOT THE SAME VOLUME CONTROL CIRCUIT. The 326S pre-amp has a higher quality volume control according to Levinson. Both the cd players and the pre-amp have "digitally controled Analog l-pad volume controls, however not the same one.
You can look at it this way. If the CDP with variable output sounded more or less the same with or without a preamp X, you wouldn't need that preamp unless you have extra sources. Preamp makes a difference in sound, and it's highly subjective to say which way sounds better. My Unidisk SC for example has variable outputs. Without preamp it sounds crystal clear and airy. With McCormack preamp in the chain the sound lost 2-3% of the transparency and 5% of midbass, but other than that it sounded pretty similar than without. With CJ tubed preamp the sound went on a huge transformation. It sounds richer, deeper, larger, and overall more pleasing. If your listening preference leans towards warmer sound, you would like it with a tubed preamp. If you like clear and transparent sound, you would not want a preamp. If you like the transparency and still need a preamp you would want McCormack. So, it boils down to your listening preference and need.
Obviously it depends on personal preferences and equipment choices. I am currently using an Ancient Audio Lektor Prime (it has one additional input and volume control) into a Deja Vu Audio 45/2a3 amp into Zu Definition 2 speakers. I like the simplicity; and to me the sound is fine - rich, full, detailed. (In the past I have also used an EAR Acute - with good results as well. It did not have the extra input, but it did have a higher output voltage which may be advantageous to some.)
I use my system for both music only and home theater. I have a ML 390s hooked into a Krell HTS 7.1 processor (which acts as my pre-amp) which then is hooked into a pair of ML 33's. When I want to listen to music only I usually run the 390's straight into the 33's and listen in two channel. I think it sounds great this way; the sound seems very transparent, open and the sound stage is wonderful. Dynamics are great this way also however this may be due to the teriffic job the 33 amp's do with dynamics. When I run the 390s through the 7.1 the sound seems much less involving. There is less of alomost everything, transparency, detail, air and even to a lesser extent dynamics. I must admit that I tend to want to blame the 7.1 as I am not sure it makes such a great pre-amp. While it is an inconvenience to have to wrestle with the cables everytime I run the cd player stright into the amp I find music only much more enjoyable this way.
My personal experiences:
1. Stuck a GNSC statement modded 270/27 straight into Krell FPB 600. Never got on with the sound. Steve Huntley recommends they got pre-ampless.
2. Later upgraded to Weiss Jason/Medea and also stuck into FPB 600. Improvement but sound seemed to lack body.
3. Stuck an AR Ref 3, vast improvement mainly with dynamics and solidity of image.
4. Friend of mine stuck his Weiss combo into Krell evo two without evo one. Sounded vastly better with preamp Krell evo one into system.
Is it sure we must check for the output impedances of the CDP, Pre amp with the input impedance of the power Amp?
And that is the so called 'matching' of the setup?