Not a MAC fan and heard the Sim 761 the baby brother of the 861. I loved the 761 and found it similar sonically to the Benchmark AHB2 but not as sterile. I love the AHB2 but the 761 was definitely a better version of the AHB2. The 761 is very detailed just like the AHB2.
If you want that detail, then the 861 would be the way to go. If you want Class A warmth or tube sound you are not getting it with the Sim. I have a CODA #16 which is a Class A amp. I would not mind having the 761 or 861 for my office system so I could flip back and forth with my Livingroom CODA #16.