I use one preamp for a tube amp and a solid state amp. I can leave the gear on (I do turn the volumes down to zero tho) and "switch on the fly". Nobsound (Yes, Chinese) makes a product line called Little Bear which makes great quality passive switch boxes which I use for the amps/preamp and one for speakers since I use the same speakers for both amps. No effect on sound quality that I can hear, they draw no power on their own. You can get them in various configurations and numbers of in/outs. check eBay. About 100 bucks each. Plenty of other brands also.