Transparent Stereo From Surround Preamp/Processor

I'll start by saying that I realize that this could have been posted in the home theater section. However, because my inquiry is truly in the interest of 2-channel stereo listening, I felt that it was more appropriate here.

First and foremost, two-channel music is my priority. Surround is secondary to me.

I have been building/tweaking my two-channel system for years, and have arrived at a place that I absolutely love, which has my DAC running directly to my power amp.

I also plan to incorporate 5-channel surround (plus two subs,) with my two channel stereo rig serving as the main L/R amp & speakers, when in surround mode.

This has been a work in progress, and I have looked at many options, in how to integrate these two. I am leaning toward a high-end pre-pro that will handle all duties, rather than do two separate systems, via theater pass-through, etc.

However, my real challenge is finding the right pre-pro, which will not compromise the wonderful sound that I get from running my DAC directly to the power amp, for 2-channel music listening, which is better than 85% of the time.

I also would not mind if the pre-pro offered a quality room correction/speaker optimization, etc. But, again, not if it is at the expense of the magic that I currently have in my 2-channel rig.

I am looking for pre-pro recommendations that, in your experience, can pass the stereo source through, with no detectable loss or sonic changes.

I am not looking for a list of "xxx is a nice sounding pre-pro." I am on a mission to find a nice sounding pre-pro ***that will not compromise the sound that I have with my current 2-channel arrangement.***

The budget is not set in stone. But to throw a number on it, I'm expecting to be in the $10K +/- range.

I look forward to your recommendations.

Thank you.
If 2 channel is your priority, I wouldn't use a HT preamp. But if you must, Maybe look at a Meridian 861.
You should take a hard look at a Theta Casablanca III. They're easy to set up and offer amazing selectivity for switching modes and switching between different interconnects.
+1 on the prior post by Zd542

There is no HT multi-channel preamp / processor that can measure up in performance to a quality built high-end 2 channel kit .... Full stop. You are looking at a compromise in two channel audio performance if you do.

Your work-around solution?

(1) Use a hi-end 2 channel integrated amp to drive the L and R speakers in two channel listening mode to preserve that audio performance excellence that the 2 channel provides.This amp will be equipped with a direct pass -through switch for the multi-channel AV pre-pro signals when it is engaged for multi-channel use = LF and RF speaker mode.

(2) Buy a quality multi-channel AV preamp/processor strictly for HT, and add in the requisite separate unit power amp(s) for the centre channel , rears, and surrounds.

Now the "primary" two channel audio performance is not compromised. Of course, this intuitively also suggests also having a separate matched high-end two channel audio source to the integrated amp, independent of the "ordinary" lesser quality multi channel AV HT spinner into the AV pre-amp/pro, that is bested suited for movies etc.
I use the Marantz AV8003 and it fits the bill. Possibly the current model would work. Highly recommended and better than the pure stereo preamp (Naim 72 with Avondale cards) that it replaced.
In my experience, there is not a processor that will NOT impact your 2-channel system.

A few great ones include the Meridian 861 (I owned one but it still did not come close to my 2-channel setup) and the Krell Evo 707 which I auditioned but again was not a 2-channel system replacement.
If stereo is important I see no reason to not have a stereo pre unless you physically can't fit one into your system. You can run the front L/R pre outs from the prepro into an HT bypass or spare input on the stereo pre and change between stereo and surround just by changing the input on the stereo pre -- this is NOT running "two separate systems." This way the prepro can run surround duties but is completely out of the loop in stereo. You also get to put the majority of funds where it matters most and spend less on the prepro that will probably get outmoded at some point anyway and need to be replaced. Not to mention the number of prepros that can do justice in a high end rig severely limits your options assuming you can even find one that meets your tastes. Just my two cents, and best of luck.
For me, it's hard to answer this question without two key pieces of information:

1) Is your two channel system 2.0 or 2.2. If it's 2.2 (subs active for music) then you have to consider how to best cross-over to the subs. Which raises the question:

2) Is all your source material digital?

If the answer to both questions is "yes", then I'd choose amongst the best pre-pros (instead of using a high-end preamp and a separate processor with HT bypass) for both music and theater because IME crossing within the pre-pro is highly likely to optimize the hand-off from main speaker to the subs. This will benefit music listening in two-channel more than any offsetting degradation within the analog section of the pre-pro, IMHO.

If the answer to both questions is "no", a good pre-amp and HT by-pass is probably your best call because you don't need to worry about the x-over function and most (tho certainly not all) folks will be happier with a high-end pre-amp for music.

If the answer to #1 is "yes" and #2 is "no", you've got a more complicated decision on your hands.