Whoop! I've managed to revive the second failed amp! When the first board failed I replaced the blown TP2050 with an STA516B at Krilli's suggestion, and when that didn't work I fitted a new TCA2002 as well. That didn't work either and the board was still dead so I gave up on it. There was nothing to lose though so I decided to desolder the chips and use them to replace the blown chips on the second failed board, and much to my surprise it works! I now feel ridiculously pleased, it's even more satisfying than building a new board from scratch
So I've got a working amp fitted with an STA516B. Now it's just a question of whether I can fit any sort of protection to avoid it blowing again, or whether the beefier power stage will be enough.