ARC LS1, LS2, LS3 , or LS7, which to buy?

Oh great and knowing Audio Research mavens, I have around $750.00 to spend on an ARC preamp. The models listed above are all in my price range. Can anyone sort out the sonic characteristics a bit for me, I have no way of auditioning any of these. Balanced outputs are not required. This is the start of a new system, so info on solid state power amps that have a synergy with the ARC preamps would be appreciated as well. Thanks, Marty.