Many questions about HT pass-through options

I'm trying to consolidate/simplify equipment in my dual purpose (2 channel and home theater) media room. The net is I want to use the same amplifiers and front speakers for both systems without recabling each time I switch.

I'm completely satisfied with my preamp (Musical Fidelity Nu-Vista) and prefer not to swap it out, but want to easily switch 5.1 (via my pre-pro) to 2 channel and back.

I'm considering a new preamp with home theater passthru, or equivalent alternatives not requiring a new pre.

My questions:

1) Exactly how is HT passthrough implemented in audiophile preamps? Is it simply a high quality switch, or is there something more to it?
2) I read in one post that the standard tape loop can be used for bypass. Is this true? Has anyone done it? Isn't there a risk to the internal circuitry of my preamp?
3) In lieu of a new preamp, is there high quality selector switch that doesn't cost a small fortune? Has anyone made one DIY, and if so, can you recommend good switch parts?

Finally - any recommndations for a good quality preamp, preferably Tube, with a really good phone section, passtrhu, and remote controllable. Budget is in the $1500 range used.

any and all advice or opinion is welcome, and appreciated