So you have a great hi end stereo preamp, but

The problem was discussed on different forums before and most common conclusion is to have two separate systems. 

you can’t funnel any sound from your ht system thru this magical box.

Uh, sure you can. With ****any**** preamp.

Millercarbon re: "The great writer Harlan Ellison, speaking of Joan Collins, said, "Her mind is a vast barren plain, across which winds play, endlessly."

She was good in his episode of Star Trek tho’

Same question opened in different threads over and over, looks familiar:
https://forum.audiogon.com/discussions/hi-end-tube-preamps-it-s-all-about-functionality

I have a stereo pre-amp & a HT Receiver with line level outputs.

HT L/R outputs feed an input on the stereo preamp. Set stereo to fixed volume (80 dB) for HT use. Calibrate HT at that level, adjust theater volume with HT Receiver.