A/V Receiver vs. seperates

Forgive my ignorance, but I have only recently started to take an interest in audio. If I only want to listen to CDs, and don't really care about home theater, will I get significantly better sound if I buy a seperate amp and preamp, or should I just opt for the a/v reciever?

Sony CDP-CX450 400 disc megachanger
Adcom GDA-700 DAC Converter
Acoustic Research AR1 speakers w/500 watt powered 15" subs
Onkyo TX-SV727 A/V receiver (the item to be replaced)
It really depends on what level you're considering, but in general for music only I would rule out AV receivers. All the extra cheapER circuitry in AV receivers will degrade music reproduction.

If this will be your first music dedicated system don't rule out a good integrated. And if you could tell us your budget and musical tastes, that would help prompt recommendations.
If you think you might get serious about stereo reproduction then seperates are the way to go. If your Onkyo has preamp outs you can incorporate a high-quality 2-channel amp and preamp(or integrated amp) into your home theater and have the best of both worlds. This way, when you listen to CDs the signal will only pass through the stereo amp and preamp and bypass the A/V receiver, but you'll still be able to use the A/V receiver for movies and other surround material. Email me if this sounds like something that might work for you.
I'm looking to spend upwards of $1500 to replace the receiver. In terms of taste, I like classic rock, enjoy female vocals (on a good recording) and listen to a fair amount of hip hop. The 500W powered 15" subs have been able to take care of the bass, but I would like it to hit cleaner. The main reason I want to replace the receiver is to clarify the sound on my rock tracks. Specifically, I am looking to improve cymbals and other "harsher" sounds so that they become easy on the ears. (Think Led Zeppelin)

Thanks for all the help.
$1500 would get you one of the better AV receivers, though it still wouldn't be quite the same as separates. Consider the Marantz SR-8200, for example.
I'm using the Blue Circle BC21/BC22 tube preamp/ solid state amp combo right now that you could probably find used for around $1500-1700 used. I really like this combo, it presents a very smooth, coherent and large sound. Although I have built my system primarily for acoustic instrument and vocalist playback, it handles most types of music quite well.
Seperates! That way you can mix and match or upgrade as you wish. Also the power you get from a reciever is half that of a sepreate at the same watts per.