I have owned the Simaudio i7 and have upgraded to the point where I now have a P-8 and W-8. I still often crank up the volume to the low 50's. Volume didn't change as I upgraded to the high end Sim separates but the quality of sound did. Still, we're talking serious deminishing returns moving from the i7 to the P-8 and W-8 separates. The i7 was fantastic and I expect the 600i is even better!
Enjoy!
Enjoy!