Hi Kareem,
• PSR-S670 has only (approx.) 32 MB of Expansion Wave Memory,
• PSR-S770 (approx.) 160 MB and
• PSR-S970 (approx.) 512 MB.
The Yamaha Expansion Manager (YEM) supports up to 128 Packs. Each Pack can contain up to 128 Custom
Normal Voices PLUS up to 128 Custom
Drum Voices (simultaneously).
This means that the theoretical maximum are 128 * 128 = 16384 Custom
Normal Voices PLUS 128 * 128 = 16384 Custom
Drum Voices (a total of 32,768 Custom Voices).
BUT of course it depends on the total Memory size of the particular instrument, how many Custom Voices can be installed.
Best Regards,
Chris
P.S.
As mentioned above, the S670's Expansion Memory is very small. In addition, the S670 has no Display-Buttons (A - J) for a quick operation. Therefore, I recommend you to choose the S770 as a minimum (better S970
).