Its a great amp to get, well i actually upgraded my 750SE to the 4600 model.
Quite a good upgrade for me and the main difference is that directional steering perception has more depth, clearer and a bit more oomph than the £400-£500 models. Saying that i had several older top end models 3090/A1 etc so its nice to get back to a simular level of surround again.
Good thing is i got it for £599 as a 2 month old shop dem unit, chuffed, makes my Sen HD600s sing too you should be delighted when you get it.