Thanks for the clarification sirquack. The problem is that on the HSU STF-2 I don't see any line-out port.

Probably then a splitter from the receiver should do it. You know the exact cable?

M80
VP160
HSU STF2 Sub
4x M3 In-Ceiling
QS10H Side Surr.
QS8 Back Surr.
3x Monoblock Amps, DEN-X4300