The following a DIY method, others will have to chime in on commercial applications
Umm, just a dual ganged rotary switch would work here. This is just two outputs going into one input I assume (one SS preamp and one tube preamp feeding into one amplifier??) I would do break than make like most normal rotary switches do, simply because a make before break is going to short the two preamps for a split second...and the short audible pop would be more acceptable than a short electronic pop.
A rotary switch will do, and are avalable from from
Mouser and
Digikey. How much they "affect" the sound is up to you...I'm grown to be alot more relaxed about the "audiophile" thing over the years. If you would like a very high quality (and audiophile approved) rotary switch, then check out
Percy Audio (page 13 on the link provided).
To put it all together, I would recommend these
RCA plugs, and this
case for a nice solid "Creek" look. Use descent 18ga wire inside, even this
16ga wire would be pretty good. This would cost you ~$100.
Enjoy