I think MTH Real Trax is O scale three rail with a blackened center rail and built in plastic road bed? If that is the case, I would do some experimenting. I think home centers sell cork tile, you might see if you can buy a couple of pieces from some open stock and just slip them under the roadbed to see if it quiets it enough. You might also try some of the foam rubber products that are made to go between a pickup bed and camper shell as a gasket. You might also try carpet tiles. I'm thinking that you should try anything you can think of that will offer sound deadening qualities. When you find the product that works, then get enough to do the job, and cut it to the exact width of your roadbed so that it supports and isolates the plastic roadbed from the plywood, but doesn't show. If a little sticks out, cover it with ground foam and scenery materials to hide it. If foam rubber quiets the track enough, AMI makes an uncured rubber road bed material. It doesn't make very good road bed, but it might make a nice rubber isolator under your MTH track. Something else I just thought of that you might try is foam carpet padding, again cut to fit under the MTH track. You might be able to pick up a remnnent from a carpet store for a good price.
As far as your question of should you use the MTH track, I model in ho, but my local hobby shop has 4 tables in the middle of the train dept. set up in a large rectangle with a number of test ovals on the tables in n scale, ho, o & large scale. They have the MTH on the tables for the o scale 3 rail demonstration. I think the MTH is about the best track you can get, although I see Lionel is copying it, and I think that type of track was probable pioneered by Gargraves.
