What you want to look for is an amp with a high input impedance(say, 35k ohms or higher). You will want as low
an output impedance on your pre-amp as possible. The reason for this has to do with transferring power, buffering, etc.
If you mix, most people I know will use a tube preamp and solid state power amp.
As far as what you might gain or lose with this setup, not much.