Ok, here's the thought: I have a Fender Hot Rod Deluxe combo. I'd like to purchase a Marshall head, mainly for the classic distortion, and be able to hook it up so that both the Marshall head and the Fender pre-amp run through the single combo speaker (with A/B footswitching if possible). This would enable me to NOT have to bring an extra cab to shows (and give me the best of "both worlds" in terms of clean and dirty tone)

I've read that with something like a "Tonebone" switching system that it is possible. Also, I read about problems with the preamp (or head) overloading when it is not "in use".

Thanks for ideas and advice!
if you use a regular a/b box, you won't be playing for long before the OT in one or both of your amps crap out on you from having no load on it

tonebone makes a switcher (headbone vt, I think) that lets you switch between two tube heads, but building something yourself could get pretty complicated if you aren't handy with relays or digital switching and dummy loads. to be honest, I wouldn't really be comfortable doing it myself

I know I've heard of a couple other companies who make similar products, but I can't remember them at the moment.. so my recommendation would be to just bite the bullet and buy the product we know works