Speakers than can run 2 different amps

most speakers made today separate mid/high and woofer connections - enabling biwiring or passive biamping (which is what you want to do). Setting up such a configuration (tube on hi, ss on low, requires that your amps be able to balance the gain so they are matched.

Bdgregory beat me to it. Single binding posts on high quality speakers is much less common than the biamping/biwiring type as described. If you try this, you have to carefully match the gain from both amops and don't forget to take off the jumpers/straps that connect the top and bottom posts.

Most bi-wired speakers will divide the terminal cross-over in the midrange. The sonic difference between the two amps will be very audible in a bad way. You would be way better off buying a tube friendly 2-way, biwire if you want utilizing the tube amp and then power a separate woofer/sub woofer speaker with your SS amp.

...and it's not just gain matching that you must be concerned with. There can be issues with impedance matching, crossovers, etc, etc. Please check out some of the other Agon threads on bi-amping before you jump in.

Here's a discussion on why you might want to just stick with bi-wiring instead (because it's good, and also easy):

http://www.vandersteen.com/pages/Answr7.htm

That said, check out Gallo Reference series and their optional SA power amp used for bass range with 3.1(&3.5?).