Nice looking unit. There may be a simpler explanation for the lack of sounds -- bad speaker. There was a crop of bad speakers from MTH's supplier, particularly the 4-Ohm speakers used in the 3-volt locomotives. I have two to 4-ohm speakers to replace, plus a couple of 16-ohm speakers that have gone south in 5-volt units. I've been looking into pairing up H.O. enclosed speakers as their sound has improved greatly over the past couple of years and there are some good places I can position them for better sound output.
As for not getting it into the remote. If the remote has been reset and completely cleared of engines, it should add. Otherwise it might have an address of an existing engine and the remote thinks it's already there. I'd also consider tethering the remote to the TIU where the locomotive is if multiple TIUs are on the layout.
Since we have multiple TIUs and there are often DCS trains running, what we've started doing is tethering the remote to TIU #1. This prevents the remote from "reaching out" to other TIUs and grabbing another locomotive and potentially changing its address (real fun). When tethered, a remote doesn't use it's radio transmitter. I've designed a test/setup bench but haven't built it yet, which will be where we will add/edit locomotives rather than on a track in the staging yard.
Hope this helps.