Hi Manuel,
I only use YEM to show me the limits of the expansion pack(s) that I can install altogether in one installation.
Using PSR-S970 as an example (I do not have PSR-S975, so I do not know its details within YEM unless I can found a PSR-975_InstrumentInfo.n27 file and import it to YEM), the limits are:
Voice Wave Size: 509 MB
Audio Style Wave Size: 128 MB
Voice Parameter Size: 3072 KB (or 3 MB)
User Drive Size: 13906 KB (or 13MB)
YEM usually takes some time (with heavy CPU usage that makes the cooling fan scream in some cases) to calculate the sizes of the selected pack(s). When any of the above-mentioned sizes turns red, that corresponding limit is exceeded and we must un-select some of the packs / voices to meet the size limit allowed for that keyboard model.
My main arranger is Genos, which has 1.8GB of expansion flash memory, and I still faced insufficient expansion memory issues due to the bigger number of expansion packs. So I had to use YEM to carefully review the combined packs are within the limits allowed.
BTW, I exchanged my PSR-S970 for a Korg Pa1000 for a different user experience, but still keep the Genos. Overall, I found that I like the Yamaha arranger experience much better, and more flexible due to the fact that Yamaha arrangers can load voices/styles from the USB flash drive directly without having to pre-load them into user area first. The process of pack installation to the expansion flash memory is just for the convenience of the users so they do not have to waste their time in loading multiple voices and styles every time they use the keyboard.
Thanks,
Paul