FWIW, I am also a (long time) Comcast customer.

Certain Comcast channel offerings *will* require their HD tuner or HD DVR box rental, not simply the converter (digital transition) box. However what you might first try is to re-scan the channels when connecting directly. It's possible a few more may come in correctly given your Aquos likely has a built-in QAM tuner for unencrypted content. Most of the HD stuff still won't be available w/o box rental though. That's how they pay the bills.