If you want to shake the very foundations of your home, the R501MKII can do it just fine, but at the expense of clarity. The S4.1 may not piss your neighbours off as much as the R501, but its sound quality is much better.

Seeing as you liked the S2.1, you could go with the S4.1.

We have all 3 units at the showroom, so feel free to drop by to give anyone a go.