best used 5.1 dd/dts pre/pro?

I'm in the process of going from a receiver to separates, and I will be moving into a new house that won't allow for 6.1 surround (the room will only allow for two surrounds).
Therefore, I thought I might be better off buying a higher quality used 5.1 pre/pro instead of spending the same to get a new, lower quality 6.1 pre/pro that I won't be able to fully utilize.

Any suggestions? I have a separate, stereo preamp for 2-channel (which I listen to 65% of the time), so the 2-channel capabilities are not of the upmost importance. But, it would be convenient to have something that sounded pretty good on stereo stuff in case I was feeling lazy. Thanks!
The Counterpoint HC808 Surround Processor and HC818 Line Stage are an excellent choice here. I use these now with great success. Each of these is in the $300-$500 range on the used market and also might still be available new at this price through HCM audio. Don't let the Counterpoint situation scare you....Michael Elliot has quite an impressive update and repair of Counterpoint products.
Hope this helps.
You didn't indicate what your budget is, so I'll stick with suggestions that are in the "reasonable to modest" range for HT pre/pros. Of the units I've heard, I'd recommend the top-of-the-line units by Adcom (GTP-760), B&K, Parasound, and Rotel. If you have more money to spend, I'd seriously consider the Bryston SP-1.
I'd like to spend no more than $1200 on the used piece. Sorry for omitting that.
I B&K REF20 goes for about 1000-1200 bucks, has DD/DTS and is somewhat upgradable.
Sdcampbell, i agree with your suggestions in that price range. Excellent work. I know this is not my thread, But am curious about the Bryston you mention. I know it is relatively new in the field and as such not too much info. on it. Could you enlighten me/us? What in particular do you like about it? Features? Pros/cons generally, e.g.,upgradable? MSRP? Nothing fancy, no full blown review is necessary, but do kick down a few lines.

I auditioned quite a few processors. It came down to 2 processors the Proceed AVP and the EAD Ovation. There are a few things to note about the EAD. The video switching is not broadcast quality (I don't use it at all) and there is no component video switching. Volume control is strictly in the digital domain and there is no bi-pass--so I run this into a pre-amp with a bi-pass for HT use. On the plus--it is upgradeable--in fact they are now offering 8.1 channel upgrades for my unit (I'm going to wait and see if there's going to be software available to make it worth while--and it sounds like that's not where you are going anyway--so a used one could be a good option). Sound quality is excellent. I found it to be smoother, better developed (in terms of enveloping the listener) and much better low level (micro) dynamics, than the AVP. The AVP was more dynamic on loud passages, but I could always pick out the speakers on the AVP. However, in your case I would give my vote to the AVP--because it has an analog bi-pass mode and the volume is all analog. If you are going to listen to stereo (particularly vinyl)--this will sound much better than the EAD.
You can probably find a used Nakamichi CA-1 with 5.1 DD/DTS option for less than $1000 (or get a DD unit w/o DTS for $700-800 and have it upgraded for $200). I've seen a few up for sale recently. The CA-1 is well built, nice looking, good bass management, and analog by-pass for surprisingly good 2-channel performance. One of Nakamichi's last products of merit.
In the course of my recent pre/pro search, I stumbled across the Anthem 5.1 Pre Pro which sounded pretty darn good compared to a lot of higher end units. I didn't consider it because its 5.1 not 7.1, but for your application, you may want to listen to it.
Chstob, The Bryston SP-1 is Brystons only preamp processor. Is is said to be one of the finest preams available for 2ch music. It rivals many of the finest preamp only systems at any price. To add frosting to the cake, i'ts got a decent 5.1 section as well. negatives? sure. it's only 5.1 and it has no video switching. Also, it's kind of expensive.