1,024 Waveforms
4,096 Keybanks

Thanks Bad Mister for response! So MOXF (with 1GB or 2GB Flash) can hold twice as much? Also, are the max numbers for both XS and MOXF given for mono or stereo samples used?

Thank you!

So MOXF (with 1GB or 2GB Flash) can hold twice as much?

Well, yes, but it is best always to recognize how the memory is utilized.

Yes, the MOXF has room for 2,048 Waveforms and that's 8,192 Keybanks but memory is full on a whichever-comes-first basis. If you reach the size maximum before you reach the number of Waveforms, memory is full. If you reach the number of Keybanks before you reach either the Waveform or size limit, memory is full. But essentially the XF doubled the statistics over XS.

In both XF and MOXF a KEYBANK can contain two samples. Stereo was accomplished with two mono samples, a separately stored L and R... occupying a Keybank.

There are 128 MIDI notes, C-2 thru G8, horizontally across the keyboard
There are 127 Velocities, 1-127, vertically by key on speed

How you setup your Keybanks can vary based on what you need to accomplish.
Say you have 5 different snare drum samples assigned to a single key, you would typically give each its own velocity range. Only two samples can occupy a KEYBANK - they could be two different things - you don't have to use the two as a stereo pair, it's up to you. Just know the limit is two samples per KEYBANK to accommodate stereo, how you actually use it is up to you.

A maximum of 256 Keybanks per Waveform.