You're right, the speaker is attached to the underside corner of the keypad bezel with double-stick tape. The cnn.cn website is crammed with 8220 replacement parts. If you go to their keypad bezel page and click the lower photo (+)Zoom link, you'll see the oval speaker attached to the lower left inside corner of the bezel.
If you look carefully at the right side of the speaker, you'll see two copper pads. Those copper pads press against two metal prongs that extend up from the backplate, completing the circuit. If those prongs got bent or misaligned during reassembly then your speaker won't work. It's also important to have the main board fit snugly in the backplate. The few times I've disassembled my phone, it took me 5 or 6 times to get the main board snapped properly into the backplate. If there seems to be a lump under the keyboard, it means the main board isn't all the way in. That might leave a gap between the speaker and the prongs on the backplate.
There is a brief, hurried video on cnn.cn's backplate page that shows how to disassemble the phone. That's more of an FYI for others reading this post, you have probably gone through the whole process already.
Keep us posted.