Ok thank you all for all of your advice and help.
This upgrade is a pretty bit step up for me (having had the 565 since before even Dolby Digital and DTS) and I wanted to make sure I was doing the right thing - especially as the 861 is really a bit too much money for me to justify.

And the 565 still outperforms anything that I have ever heard in someones actual home or personal cinema set-up.

I have ordered a G61R, HD621 and 24/96 upgrades for my 2 DSP5000's and DSP5000C - taking advantage of the Meridian upgrade program before it ends!

I want to thank everyone who chipped in with advice and suggestions (some of which I had not considered) and I can't wait to get the new kit installed and start running it in :-)

Here's hoping that Meridian don't announce a G61r replacement before the year is over!!! <fingers crossed>.