What did you add to your 2 channel system to do HT?

@carlsbad2 

That's correct.  When I run 2 channel, none of the HT components are in the signal path. 

My two REL subs have both speaker level and LFE line level inputs that can be used simultaneously with different gain controls for each.  When I do HT, they are pulling double duty. 

I replaced my surround processor, amps, and speakers with a Sony HT A9 setup for immersive sound.  A big surprise was how good Roon streamed to the setup via HDMI from the Nucleus sounds.  Ultimate decluttering.

The feature set of the Parasound P6 preamp can’t be beat for this purpose. Sonically it doesn’t seem to do any harm. No grain/grunge. Just seems to disappear.

What are you trying to get out of it? Your center channel amp is overkill! If you have a HT receiver, use the HT receiver amp for HT, then use your good amps for 2ch. For HT it is very important that all speakers are timber matched, as sound goes around the room the tone is matched just as the volume/db should be. You also have REL subs? Why not just use them and not another one? Feel like you got all the gear and just want to use it, you can most likely get better sound using less, and making it simpler. 

I have 2 separate systems, one for HT and one for 2ch. Neither does the other's job well. Will tell you when the HT is all setup correctly, it's awesome! Mine is better then most theaters. 

5.1 is good, when you step up to 7.2.4 or something like that it becomes magical. You can hear a door shut in space, as well where the plane is coming from, how high, is is climbing or diving. It trips my dogs out all the time. 

@mswale Yeah, I realize that the Adcom amp is overkill, but I had it laying around, so I'm using it.  My two-channel amp is a much higher quality Coda.

The Sonus Faber center speaker is actually fairly well matched to my Von Schweikert mains.  That was just dumb luck as much as anything.  I have an older center channel speaker by Von Schweikert and the Sonus Faber is actually a better match. 

I have two REL S/510 subwoofers that I use for two channel.  They are great for that purpose, but my larger SVS does better for explosions, etc.  It sits in the back of the room and seems to work well there. It does nothing when I play two channel audio.

I'm really not trying to improve upon the HT end.  Just explaining what I have and wondered what other people did.  I'm not a real home theater enthusiast. My two channel system is much higher quality that the HT gear.