TRS jacks are usually used for professional audio recording. This is one of those amplifiers that can be linked to a mixer board or an expensive reel to reel recorder. You can find adapters that go from 1/4" TRS to RCA everywhere. Try your local electronics store or RadioShack.
Alternatively you can order some online but it works just as well to use the tape1 outputs, because the tape2 output and tape1 output basically put out the exact same signal.
Heres an example of what those adapters would look like:
http://www.webstermusic.com/DUALGOLD_files/imageCPR400G.gif