I agree, if the power-lines are only option and it works already, go for it!
It's definitely worth asking VM to move your router but In theory, you could probably do it yourself!
You should already have the cable coming in to the front of your house which plugs in to your current cable box. You could split that cable using a 3 way splitter. One cable to the router, one to your original cable box and one to your HD51.
All the info needed to run your router and cable box is sent down the same line so it should work!
Obviously you would have to buy the cables and splitter needed, but its easy to do ;-)
Bit of a faff for you but at least you will get a hard line to the router if you find you have any issues with the power-line adapters.