In case my nickname does not show, this is treefarmer. I had the same problem and decided to fix it myself over this Christmas. I was successful, and here is what I found.
In my case, the problem lies with the volume control chip ( it has a voltage controlled amplifier, or VCA in it) on the main amplifier board. The voltage which controls
the volume for all channels comes from the right front speaker. There is an issue with the I.C., in that it has some abnormal loading (leakage) of the volume control signal at the I.C. pin. You need about 5.2 volts for full volume output, and on my system, I can only get about 1 volt. You can find the IC data sheet (Mitsubishi M51132L) here:
The parts inside the enclosure get quite hot under normal operation, and I would not be surprised
if this I.C. has an issue with degradation under high temperature. Regardless
of the problem, I managed to get the volume back with one simple fix.
If you can open up the right front speaker, place a 10 kohm resistor in parallel with R1, which should have three orange stripes, and one gold stripe. This fixed mine, but this might only be temporary, depending on how much worse the volume control I.C. becomes.
I did check out the power supply, including transformers and everything else, and they all look fine. It would surprise me if the transformer failed as has been posted in other forums. They should be able to survive higher temperatures than the other electronic components in the box, especially when most of them are consumer grade parts with a max temperature of 70 C. One thing of note is that turning off the right front speaker pretty much shuts off most of the quiescent current draw of the amplifier board. I found that with only the sub cabinet switch on, nothing gets warm. You won't see significant warming
of the interior components until you turn
on the right front speaker. However, then the inside of the sub enclosure gets pretty hot (too hot in my opinion) just sitting there with all the speakers powered up.
I would recommend at least turning off the Right Front speaker when the computer is powered down. More often if you are not listening to anything. I don't think you need to shut off the sub enclosure to keep things cool, but turning off everything ensures that the amp is not sitting there cooking itself. And, unless Altec has changed the design, I would bet new systems will fail in the same manner.
For what that's worth. Hopefully somebody will find this helpful