Low buzzing through speaks

But I would just keep using the XLR balanced interconnects throughout especially if your gears are fully balanced design or true differential design internally. I don’t know if your Mac and Sim are true differential design or fully balanced design internally, but if they were, you will be better off using XLR cables throughout as it would sound better than using RCA single ended cables. it’s quieter (lower noise floor) when using XLR cables if your gears are fully balanced design or true differential design internally.

FYI, not all gears that provide XLR connectivity are fully balanced design or true differential design internally. Some are single ended design internally although they provide XLR connectivity (outputs & inputs). Marantz multi-channel power amps and their preamp surround processors are single ended design internally but they provide XLR balanced connectivity (inputs & outputs). So if your gears aren’t fully balanced design or true differential design design internally you can use RCA single ended interconnects and would sound the same whether you’re using RCA or XLR, or you would probably be better off using RCA in this case, unless if you're running long interconnects then use XLR cables. 

@kingbr circling back to the interconnect cables between the preamp and power amp, I have a new angle to look into. As you know, XLR plugs have three pins. Two are for the balanced signal, and the third is for the signal ground. You will also note that the XLR connector body (also known as the connector shell) is typically made of metal, and is therefore conductive to electricity. 
 

There is a golden rule in electronics to only use one path for any signal. Ground connections are often the most difficult to control, because there are different approaches to grounding. But for the sake of this discussion, let's leave it at the golden rule. Normally we consider the preamplifier in a HiFi system to be the place where all grounds originate. Therefore the other things (such as your power amplifier) should not allow a circuit to form through the shield ground, which is normally also the chassis ground. You will want to also keep the signal ground separated from chassis ground at all points from the preamp to the power amp. The shield is supposed to be electrically connected to only the chassis ground of the preamp. It must not be connected to the XLR connector shell at the power amp, or an undesirable current will flow through the shield, causing that buzzing noise you hear in your speakers. 

Thank you @dilatante and definitely noted. You all make such great cases and like I said above because of so many thoughtful, helpful, insightful, and supportive replies from all of you the outcome is now secondary and if I live with it, I will sleep much better at night and not worry about it anymore. The positivity and great support has truly been not a silver lining, a gold one! Wish I could do more but a deep sincere thank you is the most I can so humbly offer...

I already have the attenuator and ground lifter (I think they may have just arrived) so I might as well try and see? But I will now listen more closely once they're in to see if I lose any signal purity. I can always return them. Knowing this is so common and that so many live with it, and yes that mine is so inaudible except ear to tweet, I have now started to enter acceptance phase😂😁🤣. And though I can't "unhear it" (love that one @dilatante😁), I can really now wrap my brain around it thanks to all of you...

Thank you @sleepwalker65 , so are you suggesting I go to RCA IC's? 

@dilatante great point on the fully balanced. I am pretty sure both the Mac and Sim are fully balanced, I know the Sim is actually and I have to believe the Mac is as well...

@kingbr 

You are most welcome. 

Usually most if not all Mac amps such as their monoblock amps and most of their stereo power amps are fully balanced design or true differential design but not sure about their entry level AV preamp surround processors such as your MX122, whish was based on the Marantz AV8802. Mac's flagship AV preamp surround processors such as as the MX 160/161/170 are most likely fully balanced design or true differential design. I have no clue regarding your Simaudio Titan multi-channel amp. 

Just enjoy your music and movies and forget about that faint buzz that's only noticeable from couple inches away from your speaker.