I'm not too sure myself on this one but someone on here mentioned if you have no phone then to get the best line stats is to use no filter at all (mk3 is a filter) as it just adds pointless resistance. With it removed then you could just buy a BT plug to RJ11, but to be honest that's for people who want to squeeze every ounce of sync rate from there line.
Which is why you should focus on why your line is not performing normally first. Do you have MyDSLWebStats, so someone can have a look at your line in further depth?
Or a few graphs particularly the HLog graph, you could upload pictures of.
When I changed to your router I was not impressed. I was experiencing strange resyncs as well at random times, and eventually switched to a Billion 8800NL in which I have had no issues with at all since. I am not saying this could be the issue but just putting that out there.
I wonder how the wiring is in your home, do you know if there is any joins from the BT Line to your master socket or if the cable is ran directly to it?