Sorry, I'm quite stuck here. Here's my current set up/approach
cable comes in to the room. Ethernet cat6 cable to the cable modem. Cat6 cable from cable modem to DIR655. CAT6 cable from DIR655 to DAP-1525, and the DAP-1525 is set to be an Access Point at 2.5Ghz. Mac connected to internet via wireless through DIR-655.
With this set up, I can 'see' both the DIR-655 and the DAP-1525 as wireless networks, and I can use the DAP-1525 signal to access the internet as well as the DIR-655. When I move the DAP-1525 to the room at the other end of the house, and connect via the wireline adapter, I can see the DAP-1525 signal, but can't connect to the internet. Have you turned OFF the wireless on the 655 while the 1525 is connected in the same room to ensure you are really connecting to the 1525 and getting internet? Need to make sure that you are actually connecting to the 1525 while in the same room as the 655 to be sure. If you can verify this and you are getting internet on the 1525 here, then move the DAP and test again with out the 655 radio being on. If you don't get any internet after you move it, then it means there is a loss of connection between the 1525, this power line adapter and the 655 router. I would review the powerline configuration and connection here.
When I try to load the admin page for the DAP-1525 in either set up, however, it still won't load.
I've also tried connecting the DAP-1525 directly to the Mac with an ethernet cable, and still can't get to the admin page.