Ash - I think we need a bit of context here if you can:
If you want specific silence duration between certain tracks you need that silence in the files. You can use media editor to add silence as necessary, and use gapless playback.
There is no way of creating a playlist that returns multiple albums and different (and customised) spaces betwen tracks without having those silences within the track files AFAIK.
But you do have some control of the intersong gaps in MC:
CD Burning - Tools/options/CD Writer - you can set the gap between tracks/crossfading etc.
Playback - tools/options/playback/settings - can set similar.
Personally I go for gapless all the time and it works good even for truly 'gapless' albums like Dark Side Of The Moon etc.
can it be done free?
Sorry I dont know what you mean.
Listening to: the hard-rocking-gapless 'Judas Cradle' from 'Beaster' by 'Sugar' on Media Center 11