Whichever one you go with I highly recommend that you do the math inasmuch as you will be running two loads in parallel. If both pairs of amps have the same input impedance you probably will be OK but if they have different input impedance I would verify with the maker of the preamp if realistically it can be done without compromise. Many of the recommendations given are tube preamps, all of which are excellent but many with limitations. I use an ARC Ref 3 and recently added a pair of JL Audio Gotham subs which I run in parallel out of my Ref 3 in conjunction with my Lamm Ml 2.1's. In order that my tube amps not crap out I inserted a Musical Fidelity Tube Buffer with its own separate power supply between the Ref3 and the Gothams. If you are interested here is the link to what I did and why
http://forum.audiogon.com/cgi-bin/fr.pl?vaslt&1049587927&openflup&584&4#584
http://forum.audiogon.com/cgi-bin/fr.pl?vaslt&1049587927&openflup&584&4#584