I was thinking along the same lines with regards to the Arcam. Changing the speakers is an option, but they need to be bookshelves. The Matrixes are front ported and seem mostly immune to room placement. My listening area is 13'x15'x9'high with carpet. Its interesting you say "room treatment". NAD's 390DD compensates for standing waves and I thought this may be an option for me. The video on the link is interesting.
C 390DD Direct Digital Powered DAC Amplifier - NAD Electronics.
The more I think about it the more I look at the speakers. Will modern day bookshelves give that much better sound then the 805"s. I would be looking at the PMC 21's or 22's or like.
Modern Rock, with some jazz and chamber music. No orchestra. I usually listen, read off the Amp, no louder than 85 decibels.
Thanks for your input.