need help all kenwood sounds like butt

[RanchFlyer]

The truck is a 72 with the stock bench and gas tank. I installed a Kenwood KRC2006 cassette deck because I didn't want to cut my dash. At the same time I installed a pair of 3.5" in the custom auto sounds dash mount. This combo sounded fine. Where things got ugly is I added a pair of 6x9 (KFC-6993PS) mounted under the seat along with a small amp (KAC-1502S). The amp is rated at 60W x 2 and the 6x9 are rated to handle 120W. At low volume it sounds fine. However if you turn it up over say 1/3, the 6x9s distort something awful.

Is this amp too much for these speakers?

Should I rewire the 6x9 to the head unit power and get a small sub powered from the amp?

If I add a sub would 2 6.5" at 60w each sound better than a single 8" at 150w