I've had only a very brief and highly non-optimal bit of exposure to the HSU speakers included in that setup (briefly listened to a pair of HB-1 mk2 and an HC-1 hooked to a very basic Onkyo receiver with a dreadful portable DVD player as analog audio source), but the combination of them and the 990/7125 should be quite nice. The HB-1 and HC-1 are pretty efficient (92dB), so the 7125 should have plenty of juice to drive them. All I can think of to say is that an 80Hz crossover is probably a good place to start all the way around (60Hz is the -2dB point for those speakers), and to let us know how you like the system once it all arrives and gets settled in. Oh, and the magnetic grille attachment they're using is pretty cool.
If you have any questions while setting it all up, you know where to find us.