IMHO the sat+sub idea is excellent but be aware that if you want to achieve very high quality reproduction of low frequencies (but I am not convinced that's everyone's target) this setup may become quite complex and expensive. With low bass, room interaction become highly important with the risk of a system that becomes boomy.
When I initially added a very good (and quite expensive) sub to my bookshelves, my system became very difficult to listen to on some bass-heavy music. The first solution was to introduce an equalizer on the sub but then the setup is not obvious anymore.
I went down this route and today I can say that I am probably not far from the limit of such a setup with dual sub, external amp, active digital crossover, digital equalizer, external dac's... but the initial price of my bookshelves has been multiplied by 8!!!
Michel