Hi, bbopman!
Sorry, I missed these posts.
What burns out the Darlington packs (Sanyo STK series) is what smokes separate transistor... excess current, usually caused by an inadvertent short. Just playing usually won't do it.
You can find most of the STK chips, or the next higher rated one.
For example, you can replace a STK1060 with a STK1070, or STK463 with STK465, replace STK080 with 082, 083, 084, 086. The only thing different is the amperage/power rating.
The problem is, these darlington packs, while convenient for the manufacturer, are generally not rated as high current (and thus power) as discrete transistors. Most do not handle more than 7 amps, but getting power transistors that will handle 25 or more amps is not that difficult.
Unless you short the speaker wires, there is not much chance of hurting one of these STK devices in normal use.
Paul