I suggest you listen to the Ayre AX-7e Integrated amplifier. See:
http://www.ayre.com/
As posted above, I also suggest you listen to the Pass Labs INT-150 and the INT-30 amps. The Luxman L-550ax Class A amp should also be added to the list. Since you already own the Sim I5.3, you should listen to their newer models.
The real question to ask is how do you make a decision. The best case would be to listen to the amps in your system and then decide. If you cannot listen with your speakers, it is going to be difficult since you do not know how it will sound. It might be better to select an amplifier that you can listen to in your system instead of guessing what amplifier will sound the best to you.
Hopefully, the comments will point you in the right direction.