Why can't I get clear sound?

I have a simple setup just to get me started in high-quality audio, which consists of a NAD C350 and Axiom M22ti's. The interconnects I'm using are cheap monster cables that I had lying around.

Now my problem is that I can't get clear sound from my audio sources. I have the speakers setup on my computer desk and I use the computer's output to play mp3's into the amp. I have many high quality rips from CDs but they sound muffled, playing a CD in the CD-Rom drive sounds muffled, downloaded songs sound muffled along with everythig else. I have even plugged in a portable CD player into the amp, my iPod and my Rio Car deck but they all produce a similar muffled and muddy sound that just doesn't sound right at all.

The only way I have been able to lessen this problem is by using a plugin for Winamp called the "Wow! Thing". When I turn this plugin on it sounds like a blanket has been lifted off of the speakers because everything sounds clear, the highs are more striking, and the bass is actually present!

I have a feeling that maybe all of the sound sources I have used are crap compared to any real good CD players. I have a better CD player, a Sony 5-disc changer, but I haven't had a change to hook that up yet, and I don't even know if it'll be any better than a portable cd player.

I just wish I could get sound the way it was meant to be heard out of my amp and speakers. For me, being still a kid and in school, the $700 I spent for the amp and speakers is quite a bit, but I'm willing to do a lot more if I can just get clear sound without having to use stupid winamp plugins and equalizers.
Have you tried playing a commercially sourced CD thru the computer's CD-ROM? Also, do your MP3s sound okay when played in the car on the Rio player?
I have tried several different store-bought CDs through my CD-ROM and CD players. The mp3s sound satisfactory though my car stereo, but that is a whole different setup. I still think that setup could be a little clearer, but there's not much you can do in a car stereo.
The interconnects could not be causing the sound to be muffled. I am not familiar with your speakers, but it sounds like maybe the tweeters aren't working. Take off the grills and put your ear up to each driver while playing music at a moderate level to make sure all drivers are working.
Your speakers and amp should sound very nice, they both get great reviews. Check and make sure your speakers are wired in phase. Most computer sound cards sound really bad so you should not use your computers analog outs for music unless it has a very high quality sound card. Hook it up as a stand alone music system with your sony changer going into the nad and leave the computer and the mp3,s out of the picture for now. Put the speakers on something that brings them to ear level when you are seated and pull them out away from the wall about three feet and see how that sounds. Play one of the cds you bought at the store. If it still sounds real bad then something is wrong with your speakers or amp. Hope this helps
What sound card are you using? If the same D/A output is causing the sound to be muffled, I'd be willing to bet that an inferior sound card is the problem. Try the Turtle or an upper level Creative Labs, and see what happens. But, in the long run, you can't expect much otu of MP3's. Cheers!

I'm currently using an onboard audio chipset, but before this I was using a Soundblaster AWE 64 and it sounded a little worse than what it currently is. I'll try hooking up the Sony deck tonight and see how it sounds. I'll also be sure to try moving the speakers away from a wall a couple of feet, and I'll check the phase as well.

Thanks for the responses.
Ok I tried everything I said in my previous post. The Sony CD changer sounded marginally better than my portable CD player, and still muffled. I did try hooking up some nice headphones into the amp though, and it sounded perfect. Not muffled at all, and the music seemed to have real depth, whereas when I turned my speakers back on they were muffled and a bit hollow. I figure that now the only things that could be the problem would be the speaker placement or the speaker wires. They are only cheap Monster Cables afterall, but shouldn't make the sound so much more drasticly worse. I moved the speakers about 2 feet away from the wall and spread then farther apart and I didn't notice much of a change. I even put them on the floor and didn't notice much of a change.

Just a shot in the dark, but what app are you playing the MP3 through? I'm assuming it's Winamp based on the original post. Does Winamp have a built in equalizer or tone controls? If so, how are they set?

How are the tone controls set in Windows? They're buried a few layers deep in the audio control panel. Getting to them takes hitting two "Advanced" buttons.
Unless I'm wrong, it seems that if the headphones worked well then the problem must be after the amp. I'm a believer in better cables so I'd try that. Try borrowing some.
I agree with Stuartbranson. The cd-changer works ok, the amp works ok and the headphones produced a wonderfull sound. Ergo: speakers(placement) or speakercables. If you wired the speakers out of phase the sound would be muffled, but also lacking any bass response. Have you tried, as stated in one of the former replies, if the tweeters were working? Is it possible to lend another pair of speakers to try with your source and amp? I don't know why, but I got the feeling the problem is with the speakers itself..... Good luck anyway.
I made sure the speakers are in phase. I even switched one of them, and then both of them together and I didn't notice a difference. I am sure the tweeters are working correctly though because I can definately hear them, and when I use that "Wow!" Plugin for winamp they are clearly heard. But I don't like that I can't get good sound without using a plugin that changes the way things should sound naturally.
A small update:

I moved my speakers to a better configuration in my room so they were about 8' apart and 3' from the walls, and were standing on some other monitor speakers that I didn't have in use (the only things I could find for stands, and they were pretty solid anyway). I think it sounded quite a bit better than having them on my desk only about 2.5' apart and about 5" from the wall. It's still not excellent sounding to my ears though, and even that stupid WOW plugin makes the speakers sound even better.

The trouble is that the speakers are useless to me when they are sitting out in the middle of my room, because 99% of the time I am listening to music is when I'm on the computer, so they need to be here in front of me on the desk. Maybe if I got a wider desk I could place the speakers farther apart, but that really doesn't help get them further away from the wall...
Go with you dedicated CD player...and dont expect CD sound quality from mp3s...