Preamp or A/V receiver???

One point of your post is of high importance. You said "To my ears the system sounds excellent, but I can never seem to be satisfied." The first part of that sentence largely answers your question. The second part is characteristic of most people that take the "audiophile" view of music, which is more about a hobby focused more on comparing equipment and searching for the best set up than about listening to music. The Adcom tuner/preamp, if after careful subjective testing seems better to you than the reciever, will, within less than a year, seem like not the route to take. Rather, a higher end separate tuner and a higher end pre-amp will seem to be a better choice. This tends to go on ad infinitum. Nothing wrong with that - it's a hobby. But as to sound - you find your A/V receiver as a tuner-preamp to be excellent, "excellent" is about as good as it gets. "More excellent" is an odd term.

Keep the KEF, Arcam and the Adcom amp, they offer the most flexibility and utility regardless of which direction you go. If you decide to go with a separate home theater Preamp/Processor stay away from Onkyo or Adcom. Also, what do you want your system to be like in 1-2-3 years as new formats and media emerge and make your purchases accordingly

Somec59: Your comments hit home to me. Although I'm not as knowledgable as most who use this site, I have heard enough equipment to think the KEF speakers and the Arcam CD player are as good as I've heard anywhere (almost). Also, while others have disparaged the Adcom GFA-555, I have found it to have honest and ROBUST power, and to have the power to drive the KEFs appropriately. I hope the Adcom pre/tuner is a good match, but the consensus seems to be I probably should have shot a little higher. I'll listen to it, compare it to the Integra, and then keep the best one til I get restless again. I definitely think that in the next few years I'll want a nice pre-amp to add to my system. Are there any reasonably priced concensus top-notch pre-amps?? Thanks everyone for the advice.

OK, the verdict is in, and it wasn't even close. The Adcom GTP-500II wins hands-down. The difference was immediate and significant. I don't know why, but the Onkyo Integra was somehow "robbing" or "sapping" my power. Upon hooking the Adcom up, the clarity and the soundstage remained great, but the bass came alive. The Adcom brings the KEFs to life, and no "loudness" colouration or attenuation is necessary. Before buying the Adcom, I felt I was going to have to buy a subwoofer to realize enough bass response. I thought this was odd, what with 200 wpc (325 @ 4 ohms) on tap. With the Adcom preamp, however, the bass is full, crisp and tight. Very noticeable change. All the clarity and stereo separation I had loved with the Integra remains, but the volume and the bass response have really come alive. At least with this "Receiver vs. Preamp" challenge, the winner is clear. And considering the Adcom preamp is not particularly "high end" (original cost $700), and given that this A/V receiver was not cheap (about $800), I can only imagine the disparity increases with newer and more expensive preamps. I'm not saying my unit is comparable to a high dollar Nelson Pass amp with Wilson Audio speakers, but my set up does sound significantly better than anything I've heard at the local Tweeter chain. I think some of those who commented earlier underestimated the Adcom's quality. This thing is housed in a sturdy aluminum chassis and is quite heavy for a preamp/tuner. It utilizes two sets of rca outputs; one labeled "Lab", which bypasses all internal filters and allows the full frequency range to reach the amp, and one set labelled "Norm", which utilizes some protective features. I'm using the "Lab" outputs (both sets gold-plated), and the results are exceptional. I'm sure a lot is due to my Arcam HDCD, but I would highly recommend the Adcom GTP-500II for any budget audiophiles out there. OK, I'm satisfied for now....