I switched from a B&K preamp to the Marantz AV8003. I absolutely loved my B&K for its sound quality, but needed something with HDMI that could excel at both 2 channel and HT. The AV8003 was my choice, falling between blowing all my money on the peerless Cary Cinema 11 or Anthem D2v, or getting decent HT but garbagey two-channel from an Integra or Emotiva and the like. Long story short, I am not missing anything; the Marantz is very similar to the B&K with regard to sound quality and character. Simply put, the HT is incredible, and the 2-channel is absolutely heavenly for something that is not a dedicated 2-channel pre. Actually, I think it competes very well with most 2-channel preamps.
Like another poster mentioned, the 8003 is superior in sound quality to the 7005. However, I have just a few complaints that I might as well mention, as they may help you:
1) The crossover is only adjustable in increments of 20hz, and only goes down to 60hz. Furthermore, it only works globally, not on an individual speaker basis.
2) With regard to HD sound codecs, Audessey can only be applied to a PCM signal over HDMI, meaning that if you want room correction, the lossless codecs (Dolby True and DTS Master) must be processed by the player. The Marantz will process a bitstreamed HD signal, but will not be able to apply Audessey. Also, the Audessey is a somewhat outdated version, not the newest 32xt or whatever. I don't care for Audessey, but I figured I should mention it because this is a common complaint.
I should also mention that I use a dedicated HTPC, and thus do not use the networking features of the Marantz.