I JUST SWAP SPEAKER CABLES CURRENTLY FROM MY TUBE MONOS TO MY UH, TUBE HYBRID MULTI CH AMP.
YOU COULD ALSO input the main ch of the rec to your pre and adjust the vol there, accordingly. If your pre has a pass thru/HT bypass, you're set, just use that pair of inputs and source selection.
I didn't care for using my tube monos for HT when ran even as main outboard amps directly from my Onkyo rec. Consequently, I bought other amps for HT purposes, and without the HT bypass... just switch spkr cables back and forth. Best deal? Nope. But it sure works good and saves me a ton of $$$.
BTW I use one set of spkr wires period. Two sets would become the same thing though... just switch between the two types, which is what I'll ultimately wind up doing at some point as I'll use one room and one pr of spkrs for both 2 ch and HT 'til I get another room constructed.... if ever that happens.