Using a genuine balanced connection is all about two things:
1) reducing any interference from outside signals that is picked up by the wire run, and
2) increasing the amplitude of the signal that is fed to the speaker input.
The first is really only something that comes into play with long wire runs (think a live concert in a stadium or outdoors). Not an issue at all in your setup.
The second depends on the efficiency of your speakers. You generally get a 6-10 dB gain from using a genuine balanced connection. If your speakers are inefficient, this can really help to increase their output with your reference signal. Those KRK speakers do not have any output or efficiency problems, however. And you are listening to them nearfield (as intended) so more output is really not required.
In effect, you have no real need to switch over to a genuine balanced connection. A line-level RCA output is fine in your situation.
There are two things that I would recommend in order to improve your setup:
1) decouple your subwoofer.
You appear to have some sort of mat beneath your sub, but it looks very thin and does not appear to be an actual decoupling device. If I'm wrong about that, then ignore this suggestion. But you are obviously familiar with the benefits of decoupling - since you are using Auralex MoPads beneath your monitors. So decouple your subwoofer! An Auralex SubDude or GRAMMA is what I would recommend. Easy, inexpensive ($50) upgrade that will give you "tighter" bass with less added room distortion, reduced "rattles" and room reverberation and a drastically reduced "bleeding" of bass into other rooms of the house.
2) Passive room treatments.
I do not know the extent of your current room treatments, but the biggest benefit to you at this point will be to improve your acoustic environment. I would highly recommend GIK Acoustics for very affordable and effective passive room treatments.
The front wall (behind the front speakers) should be absorptive so that you are not hearing any "back wave" reflections - only the sound coming directly out of the speakers. This will reduce any time or phase interference from the reflected sound coming from the front of the room.
Your first reflection points (side walls and ceiling) should also be absorptive - again, to reduce any room reflections so that all you hear is the direct sound from your speakers.
The back wall directly behind your listening position should be highly damped and absorptive. The sound from your front speakers should "wash over you" and then "disappear" behind you. You do not want any sound bouncing off of that back wall directly back to your ears.
The back of the room (walls and ceiling) should be diffusive. You want to retain some sound "energy" in the room. This is not a recording "booth" and it is not an anechoic chamber. You do not want your room to be "dead". But you also do not want any "slap echoes" or direct reflections. Use diffusive panels to "scatter" the sound. This keeps the sound energy in the room, but does not allow any strong, direct reflections.
GIK has you completely covered for all of the products you will need in order to do this upgrade.
You will also want to place bass traps in the corners of your room. Start with the four vertical corners of your room and worry more about placing bass traps in the wall-wall-ceiling corners than the wall-wall-floor corners. You can go whole hog with bass traps - lining all of the edges of your room if you really want to reduce all of the various standing wave patterns that can crop up in any given room. But the vertical corners at the top are the worst offenders and you should definitely place bass traps in those four corners.
Again, GIK has you covered. You can use their Tri-Traps for a nice, snug fit. Or, if you want to keep the cost down, just straddle four of their 244 bass trap panels across the upper corners of your room.
3) After those important upgrades, the only other thing I would suggest would be to upgrade your subwoofer. Choosing a subwoofer that can truly reach down to 20Hz or lower will fill in the last tiny bit of frequency spectrum that you are not getting with your current subwoofer.
My highest recommendation would be the HSU ULS-15, which is a sealed 15" subwoofer with genuine, fantastic output down into the infrasonic 16 Hz range. Magnificent for nearfield listening!
Hope that helps!
