I recently did a very inexpensive (about $35) upgrade to the sound on my Time Machine and it turned out great. Before I get started I want to express thanks to fellow Pinsider TheKorn for his help and suggestions with the board work described below. There is no way I would have attempted this without him!
Pyle speakers were installed: A pair of 4" coaxials in the head and a 6" subwoofer in the cabinet. The subwoofer went right in with no alterations. The stock speakers in the head unit are 4" x 10" and are a little tougher to find (and more expensive) than the 4 inchers, so it was necessary to cut an adapter out of a 1/4" thick piece of wood, which was then painted flat black. I used plywood because that's what I had lying around. Hardboard might be easier to work with and paint.
To get more sound to the subwoofer I removed R10, put in two machined sockets and plugged in a small daughter board containing the original 180 ohm resistor and a 1k ohm trimmer connected in series. The daughter board also has two 10 nfd capacitors (in parallel to get to 20 nfd total) across the total resistance. The trimmer is adjusted to about 1k ohms of total resistance. The capacitors are apparently there to limit the sound to only low frequencies going to the sub. How does that work? I don't know but I read about it on another thread so I thought that I would give it a try.
Note that the pictures of the board work show 1) BEFORE - with R10 in place, 2) R10 removed and sockets installed 3) The daughter board plugged into the sockets where R10 was located. I also socketed the 180 ohm resistor on the daughter board. If I want to reverse this hack, all that is necessary is to unplug the daughter board and plug the 180 ohm resistor back into the sockets at R10. I have also saved the stock speakers so those can also be put back in, if necessary. None of the speaker openings were altered.