Sorry, I haven't been on here in a few days and missed the email.. I'm going to try and hit the fundamentals with this post. You likely know some of it based on your previous posts, but I'm going to pretend as though you don't.
The MacBook Pro can only produce an unbalanced signal... in the 1/8" TRS the tip is left, ring is right, and sleeve is ground. Same goes for 1/4" TRS when it's used for stereo signals like studio headphones. The TRS on the back of a studio monitor, however, is looking for a mono balanced signal, so tip is hot, ring is cold (reversed polarity of the hot signal), and then the sleeve is still ground. XLR, in this case ("XLR" can be used for other things in audio and lighting, but that's beyond the scope of this post), is exactly the same as TRS in that pin 1 is ground, 2 is hot, and 3 is cold. 1/4" TRS and XLR are entirely interchangeable (at least in this use case), and there would be no advantage of going with one over the other (again, in this use case).
So the MacBook Pro produces and unbalanced signal, but the monitors are looking for a balanced signal. So what does this mean? If you were to use an 1/8" TRS to 1/4" TRS cable, when the signal hits the studio monitor the signal on the ring conductor gets the polarity reversed before it is amplified. So you will have the left channel going into the speaker in phase, and the right channel going in out-of-phase. Simply put, anything that is center panned will cancel out, and everything else will sound, well, out-of-phase. To overcome this, you want to use an 1/8" TRS to 1/4" TS cable, where the R conductor from the MacBook Pro side is not wired up or simply sent to ground. The 1/8" TRS to split RCA you are using is currently doing this.
There is no advantage or disadvantage to sending the TRS connector on the monitors (or the XLR for that matter) an unbalanced signal, as compared to using the RCA inputs. You know, aside from RCA cables often being cheaply made and going bad after little use.
And if you plug in a TS connector to a TRS input, it will short the R to ground on the input and you won't have any issues if you went that route.
The ideal setup would be an audio interface with balanced outputs.