Low buzzing through speaks

Good point @markmoskow. If it already isn't the case @kingbr, try turning off all lighting in your place, and see if this makes a difference. I also agree with @dilatante. There are sometimes trade-offs in the audio world. In your situation, you will probably be *slightly* compromising the performance of the Transparent's when inserting any other device in them (like the attenuators or XLR shield lifters). Only you can decide what you want to live with. If this was my setup, at some point I would have shorted pins 2 & 3 on one of the XLR cables (at the female end, while plugged into the Sim), to see how much of this is being picked up by the cable alone. 

Agree with @dpop as it will be tradeoffs because you will be compromising the signal purity thus overall sonic fidelity (sound quality) everytime you insert something in the signal path. 

@kingbr 

I wouldn't get any XLR attenuator or any sort in the signal chain because you will be compromising the overall sound quality of your system slightly. Just leave it the way it is since the faint buzz is only noticeable from like couple inches away from the speakers anyway and has no impact on overall sound. Don't sweat it. 

So it would appear switching to RCS’s won’t make any difference, no?

The RCAs will be 3db down from the XLR connections. 3db might be enough to knock down the hiss a bit. 

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.