I don't think there will be a problem driving the speakers, but....
While the Polk was a great value in its day (IIRC - and it's been a long while), it always struck me as just a bit soft in the bass. Similarly, the ST-70, while a really great amp in many ways, is not the last word in bottom end grip. So....while this might not be a match made in heaven, I'd still think it would be kinda cool.
Marty