Need multi-channel that's great on 2 channel

Yes Jeff, it is a recurring theme everytime the question is asked. The majority of responses will be to use a 2 channel preamp with an HT Bypass feature. I am also firmly in this camp finding the 2 channel pure direct modes of most AVR's sadly lacking.

If your adament about a one box solution though, The Arcam 600 you mention is about the best out there for 2 channel reproduction from an AVR. But if you can consider adding 1 or 2 more boxes in your installation you will find that at the 600's price, it can be bettered for a lot less by using a 2 channel integrated w HT bypass or a 2 channel preamp & power amp. Again, the preamp must have a HT Bypass feature. And there are many, many quality models available to get the job done right and blow away even the Arcam 600.

Your Marantz 7005 is a fine AVR and can still be used to power the center and surrounds when listening to multi-channel sources along with its room correction facilities for multi-channel. No need to replace it for it. I use a mid level AVR as a pre/pro also but for my 2 channel listening, I have a 2 channel preamp w HT Bypass and a power amp. The best of both worlds in one clean installation. Good luck.

There are so many different ways to go Jeff. Since we don't know budget, I'll assume up to 5K, the price of an Arcam 600.

Here are just a few solid state preamp/power amp combos you can look at starting in price low to high. All the preamps have HT Bypass and will provide plenty of power to drive your B&W 805's. I am sure others can give their recommendations too:

Parasound 2100/Parasound 2250
Parasound HALO P5/A21
Atoll PR100SE/AM200
Primare PRE30/A30.2

Interested in tubes? Look at the Rogue Audio Perseus preamp and couple it with a Rogue Stereo 90 power amp or Rogue M150 mono blocks.

Want to bi-amp? Since you like Arcam, you can also consider their A38 integrated (has HT bypass) and a P38 Power amp.

Finally, don't forget a wide variety of integrated amps with HT Bypass that will do the same as the above combos but with only one box. Some good ones that come to mind are the Marantz Reference PM15S2 and the PM11S3, Creek Destiny 2 and the Music Fidelity M6i.

All above combos and integrateds should be well below the cost of an Arcam 600 with the exception of the Rogue tube mono-blocks that would be about $5500 for preamp and amps.

Good luck and have fun!