Slight buzz through speakers

So let me understand your minimum setup.  You have your McIntosh preamp plugged into your Simaudio power amp and your speakers are connected, but nothing else, right?  Does the McIntosh or Simaudio amp have a three prong plug on the power cord?  If so, use a ground cheater adapter that converts three prong to two prong.  If the buzz goes away, then the problem is line leakage and bleed in.  There are two ways to fix this - first, the ground cheater is not a solution, as it leaves the chassis ungrounded, which could become an electrical hazard.  Jensen makes a galvanic isolator that will eliminate the problem, see this link:  

They make it in mono and another one in stereo and mono for subwoofers, too.  Another option is building your own by putting two RCA connectors in a plastic box, connecting a capacitor from center pin to center pin and another one from ground to ground. The caps need to be at least 2 uFd and polyproplyene.  If you use a metal box, then the input RCA jacks must be isolated from the chassis but it is okay to ground the output RCA.  

Hi @spatialking thanks for replying. So I have my McIntosh preamp plugged into my Furman Elite 20PFi power conditioner (along with everything else except the Sim amp). I have my Simaudio amp plugged directly into the same wall outlet as the Furman Elite. It is a dedicated 20 amp line. So on that dedicated 20 amp line the Furman is plugged into the bottom receptacle and the Sim amp is plugged into the top receptacle. Both the Sim amp and the Mac pre have 3 prong plugs-the Sim is a C19 20 amp power cord. 

Just this morning I tried unplugging the McIntosh from the Furman and then plugging it directly into a different wall outlet altogether. No change buzz still there.I also removed all of my Transparent Plus XLR IC's from the McIntosh to the Sim amp (McIntosh still plugged into the Furman at this point). I completely removed the XLR IC's. So the only thing connected to the Sim amp was the speaker cables. And no buzz. This confirmed the buzz wasn't coming from the Sim amp (and I never had this buzz before so I knew it wasn't the Sim amp).

Just this morning I also unplugged every component 1 at a time from the Furman. Buzz still there so the buzz isn't coming from any other component so it has to be the McIntosh preamp, right? 

I have never plugged to Mac into the amp directly, not even possible.

Thank you for the suggestion of the cheater (many others have suggested this-I will try that). I will check out the Jensen piece you reference. I also ordered the Hum-X which will arrive tomorrow and I'm really hoping plugging the Mac into the Hum-X and then connecting to either a different wall outlet or the Furman-I'll try both and see if either works.

Again the buzz/hum is very faint and can only be heard without anything playing and putting my ear within a couple inches of the tweeters, But it was never there before and changing volume does not change the buzz it remains low (thankfully) and certainly not at all audible from the listening position...

While I applaud all your efforts and certainly sympathize, the best/easiest thing to do at this point is to call Mac and see what they suggest.  I personally am not a fan of Mac products — just not my taste — but they’re a quality company and expect they have good customer support and care about having happy customers.  Best of luck!