Ok, so I may be moving towards the end 2018 early 2019.  I'm looking for a space that will accommodate both a 2 channel stereo setup and 9.2 Dolby Atmos/DTSX setup incorporating my existing 2 channel audio components.

Most of my watching will be streaming from a NAS or online services such as Amazon Prime, HBO-GO, Starz Online and Showtime.  With about 10% or less through a traditional cable box.

I've been out of the Home Theater game for quite a while and enjoy watching movies on my Decware/Omega 2 channel setup with my PC a NAS and McIntosh D100 2 channel DAC.  If I get a new space I would like to try an entry level 9.2 setup and use it in combination with my already stellar Decware/Mac/Omega combo.

My question is ~ if my PC USB out is going to a 2 channel DAC how can I incorporate a 9.2 system into my PC as well?

I have:

1 HTPC that I would use for movies and music with JRiver Media Center
1 Decware Taboo MK II
1 McIntosh D100 2 channel DAC
1 McIntosh C200 2 channel Preamp
1 Rega RP6 TT
2 Omega RS7 Loudspeakers
2 Rythimik Audio Servo Subs
1 Cable Box

In addition I plan on buying 4 in-ceiling speakers, a center channel and 2 rear surrounds and an entry level 9.2 Home Theater Receiver such as the Marantz SR7011.

My current configuration looks pretty much like this:

HTPC (streaming from NAS or online music and video services) > D100 DAC > C200 Pre > Decware Taboo MK II > Omega RS7 Speakers.

I want to continue using my Mac DAC/Mac Preamp/Decware amp for 2 channel music, but then use a Home Theater Receiver when watching movies (but still using the Taboo for left and right channels and the Reciever will power the other channels).  I understand about Home Theater Pass Through and being able to use the Tape Loop on a Preamp if it doesn't have HTPT, but I guess what's confusing me is ...

Because I'm using USB out from my HTPC to a 2 channel DAC ~ will the DAC somehow pass a 5.1 or higher playback signal to my Preamp and then send the signal to the Home Theater Receiver and the HT Receiver will somehow know that it's 5.1 or higher playback signal?  Or am I going to need to find another DAC or a Blu-Ray player with DLNA capabilities as an additional source?

Gosh I'm little confused if I'm even posing the question correctly  let me know if that question doesn't make sense and I'll try to rephrase it somehow.

Thanks in advance!

This is very easy but you're thinking of it backwards.  Your 2 channel system still stands alone and then you incorporate your 2 channel system into your 9 channel system.  

For the front 2 channels of you AV system, don't use the 2 front channel amps in the 9 channel system.  Instead, run a pre-out signal to a pre-in signal of your 2 channel system. Calibrate the levels just like you would with all 9 channels hooked up.

To do this your 9 channel amp must have pre out availabe.  My denon 3700 does.  Your 2 channel system must have a pre-in set of inputs (bypasses the gain control in your preamp).   All 2 channel systems should have this but many don't.  I don't think decware amps have it but I'm planning to ask if it can be added if I order an amp.  Pre -in is also called "direct" or "HT Bypass".

Some who don't have a pre-in on their 2 channel system try to use a regular input and just turn the 2 channel amp up all the way when using it for HT.  Eventually they forget to turn it back down and if lucky nothing is damaged.

Jerry