A/D input AND MODX outputs are unbalanced. Don't use balanced cables. There's nothing gained - and possibly issues depending on how the "wiring"/circuitry is done on the other end.

IF (and remember MODX doesn't have these) the connections were balanced then it would be OK to use unbalanced. You could use either. What you loose by using unbalanced is noise rejection. You have a chance of adding noise to your signal using unbalanced and the longer your cable length - the more "antenna" length you have to pick up on noise. Limiting your length on cable limits your exposure - but there are certain "aggressors" (noise sources) that are strong enough to inject noise on a short run if you cross them where a balanced cable may be able to reject the same noise source even at longer lengths.

I have a Montage (which does have balanced outputs) and initially used balanced cables live - but QUICKLY reverted back to unbalanced because the live sound engineers I use have a formula for keyboards and sending them a balanced feed was against the grain. Even giving them an XLR (and that's their standard interface) was a problem since the formula says drop a DI box for keyboards. I gave up trying to go against the grain and have I believe 15 feet of unbalanced cable usually wrapped in a circle around the DI box because I only really need 5 feet. The keyboards still sound fine and I don't perceive, in live use, there's any compromise using unbalanced week-in and week-out like this.

Your HS5 and MODX are fine with unbalanced cables. If you were ultra concerned about noise rejection in the studio you could get a converter from unbalanced to balanced and have an ultra-short run from your keyboard to the conversion - then run balanced cables to your HS5s.

Here I have HS7s and find there's noise introduced by various aggressors but I believe the weak link are the unbalanced runs from my gear to the mixer (which is actually a USB sound interface with mixing capabilities - no computer needed). My feeling is really that it's the "mixer"/sound interface itself that's the issue. It's a relatively cheap brand and I wouldn't be surprised that shielding and PCB design for noise isolation is not on the top of the list of such an inexpensive piece of gear. It'd be easy to test by a more direct connection balanced to the HS7s and use the same aggressors to see if noise is as loud.

Summary is do not connect balanced TRS cables directly to MODX since it doesn't have support for those and it's bad practice to just stick a balanced cable into an unbalanced input or output.

I think some wires got crossed there @Jason -- Yotam asked about Montage and not MODX.

Hey I have Montage and not MODX... in this case still use only unbalanced cables? even with monitors? I know the HS5 have XLR socket is it better to use XLR>TS or just TS>TS normal? thanks again

Yeah, I originally answered for Montage but somehow got off track and edited my own message for MODX. Not sure what happened there.

For A/D - don't use balanced these are unbalanced connections.

For Output - You can use either balanced or unbalanced. Either will work. Balanced gives you noise rejection as described. Both your keyboard and HS5 support balanced TRS so that's the best connection to enjoy the noise rejection properties of balanced cable. But unbalanced cabling works fine although more susceptible to noise injection.