Do you use a preamp in your HT system to improve sound?

No sorry.   Rogue RP-7 part of 2 channel system. 

A Bryston SP3 processor takes in HDMI and passes balanced analog front LR to a by-pass input of an Ayre KX-5 Twenty preamp.

Dbphd,

curious to know impact to HT sound due to preamp?

First, get a good sounding processor. A lot of them are thin sounding, lack dynamics and bass. Anthem is not one of them. I’ve had bad luck with Onkyo and Emotiva, and find Marantz bright to harsh.

I also really llke Theta Digital, but it's hard to tell if they are even in business or not.

Second, they do make stand-alone tube buffers that can add the tube glow.

I have a mixed 2 channel / HT setup.  I use a Herron Audio VTSP-360 preamp for 2 channel.  None of the home theater components are engaged when I listen in 2 channel.  A home theater processor wouldn't hold a candle to the VTSP-360.

The VTSP-360 has home theater bypass, so I can use my main speakers and subwoofers and my monoblocks that I used for 2 channel in the home theater system also. 

Best of both worlds, unless you have room and budget for a dedicated home theater and a dedicated 2 channel system.