Dave,
A couple of weeks ago I helped a customer with a Seleco 800 CRT upgrade his cinema to Blu-ray when he was faced with the same dilemma.
Our Blu-ray source was a Marantz
BD8002 so money was not a major concern. His dealer also installed an Audiolab 8000AP processor to take care of HD audio decoding duties.
What I installed for him on the vision side was a s/h Lumagen scaler (Vision DVI) plus a HD Fury II. The Lumagen cost less than £200 and has a couple of HDCP compatible DVI inputs, 2x Component, 2x S-Video and 2x Composite inputs.
I know you have the Deuce. It was good at the time but things have moved on. With a projector as good as an 808 Graphics you really should be running custom resolutions and higher refresh rates. I set up the Lumagen to run Bluray and NTSC at 72Hz*, TV (Sky HD) his HD Cam at 75Hz, then some an NTSC video preset at 60Hz. The extra solidity from running a higher refresh rate makes the picture look rock solid and also helps reduce motion judder with NTSC film based DVDs. The 808G needs a scaler with a little more headroom - a Lumagen HDP or HDQ or similar from Anchor Bay would be a good match.
[*round figures]
The Lumagen also has additional tools to help with colour balance. After I'd done a bottom to top set-up of his projector, dialled in some custom resolutions to get the projector running sweet for each refresh rate, then colour balanced for each source we finally sat down to watch some stuff.
Roger was suitably floored by the picture quality from his HD sources. Casino Royal on Blu-ray looked absolutely stunning: stable, detailed yet smooth, and with a great colour palette. He was equally blown away by Sky HD. His point of comparison was the plasma with Sky HD in his other house in London. The projector image at his country house was miles better despite us standing five foot back from a 7ft wide image. Regular TV and DVD also benefitted from the makeover.
So, do you have to junk the 808 just to go HD? I'd say no.
This is the third HD CRT system I've set up in as many months (Lumagen + Barco 1208 in Derby, Lumagen + Barco 1209 in Wrexham, Lumagen + Seleco 800 in Sussex). All have been a job of work to do, but the end results have been well worth the effort.
Re the JVCs...I've calibrated JVC 350s and a 750 with Blu-ray, DVD and TV sources. They're good projectors for the money and incredibly quiet too. We all know about the colour management issues with the 350; it's one reason why the 750 was introduced. What is less well publicised is their limitations scaling TV and regular DVD. They really need the help of a scaler if you want to throw a variety of source material at them. You need to be looking at Lumagen HDQ or similar as a minimum.
Regards