First World Problem in need of Solution


My problem is that I would like to upgrade my system to a 5.1 system however I am worried about matching sound to what I currently have. 

Gear
AMPs Luxman M-900u run as mono blocks
PreAmp Luxman C-900u
Subs - SVS SB4000 - these are run via XLR from PreAmp to Sub so listening is speaker A+B
DAC PS Audio Directstream 
Fronts Focal Sopra N 3 
Rears Focal Sopra N 1 
Center Focal Sopra center

Possible Solutions 
1)
Buy a HT Processor and run rear and center out of it and use the HT Passthru on the Luxman Preamp. 
Concern
Sound is going to sound different from the rears and center than the front left and right
Thoughts: This seems like the best solution because my 2 channel listening will not be compromised

2) 
Buy a HT Processor and run rears and sub out of it. Convert the mono blocks into a normal 2 channel amp and run the center speaker into a dedicated amp. Or I could run front and rears off of the mono blocks and the center off of the the HT Processor 
Concern Potentially losing the subs in 2 channel listening. Center sounding off. The N. 3 only have one amp drive them
Thoughts: This just seems like a nightmare

3)
Sell all my gear and replace with another brand that also has HT lineup so I could accomplish all of my goals
Concern: 2 Channel Listening is going to be compromised
Thoughts: Maybe the best option? 

4) 
Scrap the 5.2 and go to a 3.1 setup. Run an optical out from the TV to the DAC. Run the monoblocks as regular amps. 
Concern: 2 Channel listening compromised, NO BASS! Unless I could run them out of the DAC? Maybe
Thoughts: UUGGGGHHH

Can some of you who have more experience weigh in on which way you would go or which option seems "best to you".

Also any suggestions for HT processor would be helpful. 

Thanks  in advance 

G
atownkeep
If 2-channel audio is your main priority, then your Option #1 is most likely the best solution.  There isn't going to be any HT Processor that is going to sound quite like your Luxman C-900u preamp.  You could go with your other options, but like you said, 2-channel audio is going to be severely compromised, especially if you are using the subs to "add bass octaves" to the natural bass of the Focal Sopra.  Everyone who runs a "hybrid rig" is compromising in the 5.1 HT side of things, but that's a necessary evil.
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If you did replace the amps, I would be very careful about matching.  Your Luxman amp is likely a very good match, along with amps such as Pass Labs (especially the XA series), maybe Parasound JC1 with high-bias Class A setting.

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For processors, I'm partial to Krell S1200U because of the Class A analog stages, but it is discontinued and does not support the new features, such as 4K video, HDR, Atmos, etc.  There are others, but for home theater movie excitement, probably the Krell Foundation is the best way to go.
Agree with comments above that option 1 is best and that you’re not going to find a perfect match for either your amps or preamp. With that, I’m just going to dumb this down a bit in an effort to simplify things. This assumes you’re not looking for absolute state-of-the-art surround performance and would be happy with very, very good 5.1 sound that doesn’t compromise your 2-channel performance in any way. Given you’re not going to perfectly match your current electronics anyway, what about buying a very good A/V receiver with a warmish sound? This way you’re at least keeping the general character of your electronics intact, and you’re getting all the amplification and surround processing you need in one relatively cost-effective box that can be easily and economically upgraded as technology inevitably progresses. Here’s an example of an AVR that might fit the bill nicely...
https://www.accessories4less.com/make-a-store/item/marsr8012/marantz-sr8012-11.2-ch-x-140-watts-netw...

While this will not be a perfect solution to your situation, it’s hard to believe this setup wouldn’t produce a highly satisfying and involving 5.1 experience. And there’s no guarantee you’ll get a much better match by going through the time, effort, and considerable expense of finding a suitable separate prepro and multichannel amp. Obviously if you’re after SOTA multichannel performance it’s worth going down that rabbit hole, but if not I think you could be very happy and maybe even pleasantly surprised with the performance of this setup (along with the several extra thousands of dollars you’ll have in your bank account). Just another option to consider FWIW. Best of luck in your quest.

Thanks guys. 

That was my feeling the best option was however finding the "right" match without going through 12 AV All in one is now the key. 

I love my Luxman gear and do not want to part with it however I do not have the room to have multiple systems. 

Marantz is where I originally started my journey in HiFi.

Is there a minimum wattage I should be looking for for the 3 Channel? 

Thanks again for your input everyone. 
You probably want at least a couple hundred watts per channel.  The best solution would be to find more Luxman amps, but they are definitely very expensive!!  I don't know if you can find a smaller M-700u that you could run mono for the center channel.  Then another M-700u for the surrounds.  Be careful when buying these from Japan because the "Japan" models are usually wired for 100V A/C (which will not work properly in the US 120V standard).


Or you can try to put in a Pass Labs or Parasound amp.  Pass Labs does not make 3 channel amps, but Parasound has an A31.  Or use a Parasound JC1 for center and an A21 for surrounds.  The JC1 can be switched to high-bias Class A which may sound closer to the Luxman signature.  Or you could try a McIntosh 3-channel like the MC303, but the McIntosh will likely be a smoother sound than the Luxman/Pass/Parasound signatures. 
I would also vote for option #1 running your 2-channel setup in bypass mode. While watching films and TV, you'll be less sensitive to differences in the sound between your mains and other speakers anyway, and this won't compromise your 2-channel playback.

Ignoring the sound character for a second, you should pick an amplifier's power output for the other three channels based on how hard the speakers are to drive and what volume you want to achieve. I'm using a Bryston 21B3 as a 3-channel amplifier, as it is one of the few 3-channel units that is capable of high power output and drive.