C421C, from what I've Googled the Phase Linear 400 has good performance to be used as a bass amp. Wattage, current, and damping factor.
Sure there are better today, but what you've got is ok for bass, mids and highs are most probably rubbish.
Just use it as I've outlined above and all your up for is the $49 for the Schiit passive preamp, I'm sure you'll be happy.
Then later on get a better amp for the bass, maybe a class d, as that's all their good for as well.
Cheers George