My friend lent me his pair of Yamaha HS50M monitors to output my Roland pt-3100 digital piano (2 x speakers to L and R phone output). He instructed me to buy balanced cables for the setup so I bought two Hosa balanced XLR-to-TRS (speaker-to-piano) cables, but I'm getting nothing, only the output from the internal speakers of the piano. What am I missing here? Should be an easy plug-and-play. I've tried turning on the piano and speakers in different sequences, checked nothing is plugged into the headphone jacks, and made sure the gain is turned up on the external speakers. Wrong cables?
You don't need balanced cables for this. You can use two standard instrument cables (electric guitar cables) and go from the 1/4" out left and right into the 1/4" input on the monitors. Make sure you are connecting from the Output jacks on the keyboard and not the input jacks. (I've made this mistake before. Hard to read the raised black letters...)
The level should be up on the powered speaker, and from the vague description in the owner's manual for the piano, you may also have to turn the volume up on it as well.
The manual is confusing. It speaks of 'phone plugs'. The stereo output actually appears to be a pair of 1/4" jacks. It is unclear whether they are TS (unbalanced) or TRS (balanced).
The Yamaha HS50M has a matching jack input. I suggest you use it.
It probably is balanced, but it really doesn't matter. Use a pair of ordinary 1/4" jack cables. TS will be fine, if you have TRS ones lying about they'll almost certainly be OK too.