How do I hook up 2 preamps to one amp

"This is the way I did it" All my parts came from Radio Shack. You can use expensive "audiophile" parts if you desire. First I constructed a small wooden box to house the parts. After I sanded, stained, and shellacked the box; it was quite attractive.

Next I drilled holes for the small red rectangle rocker switch and six female jacks. After installing this, I soldered wires from the jacks to the switch; L & R in from each pre, and L & R out to the amp.

I now use that same box with the 6 female jacks and rectangle rocker switch on another project.

I agree with Herman after all. Why use the NAD at all? If you need it for phono, just sell it and buy an NAD phono. THey are cheap. Go with the Lex only.

I have a similar situation with an older Rotel processor and Denon receiver. I was going to try this method but then thought about the sub. I want to listen to 2.1 but also have the sub available to the Denon for movies. Any suggestions?

I have a Luxman CL38U SE and a Krell Showcase processor for movies. On my Bryston amp I hook up the RCA outputs to the Luxman and the Balanced outputs to the Krell. I just flip the switch on the amp. I've had tube preamps for years and this saves tube life on the preamp as HT pass through requires having both preamps on.