Slightly OT but one thing I did notice on the S7 test track was the foam underlay under the track, very similar to laminate flooring underlay, it was just soft enough to take out and acoustic sound from the baseboard and firm enough to not flex too much when large 'heavy' tank locos (JB's L1!) passed over joints. The reduction in acoustic hollowness and sound damping were impressive and add weigth to my thinking of following suit and also adding the same stuff under the base board to cut down on the famed hollow base board noise.
The flexing looked quite prototypical at rail joints, the real thing moves quite a lot when locos pass over and the flex in the foam should reduce the dreaded wheel bounce from track not laid microscopically level LOL. Whether the track will still flex once it has been ballasted is another matter and the critical bit will be the shoulders which may need some sort of rubber-isd adhesive to still allow a little flex, or if the shoulders are wide enough then the foam under the track may have enough give any way. The S7 track was stuck onto paper which will stop any adhesive permeating into the foam and sticking it all solid.