Ok, well, the tweeters did the trick, it now sounds really good. I figured out how to mount them where the old ones were located, by cutting away some plastic and securing them with two tiny screws each. Here are a few pics.
Attachment 14283Attachment 14284
Next task is to connect to the head unit pre outs. I had the back open and looked at the back of the head unit but decided to wait for another day. I might just intercept the pre outs there and connect them to the headset outputs, thinking I can avoid running a bunch of cable to the new amp. This way I should get my AVC back. What do you think, Jimmytee?