Hello,
my opinion is, of course you can use only power amp.
But, volume control pots in Shindo amps are intended only to match output signal with preamp and speakers. Those are small pots, not convinient to everyday use. Also you are soon going to get mad trying to adjust channel balance every time you change the volume. Those small pots are sensitive for small movements and often you will have to go second, third time to get the volume and channel balance right.
Shindo preamps give you harmonically richier sound, so I would think of preamp/amp combination as a final solution.
Cheers,
Greg