I’ve just found excellent little program for windows and mac
Elektron C6 SysExManager / local copy: mac windows
This software can upload wav and aiff samples to ANY hardware sampler that supports SMDI transfer protocol by MIDI cable! Designed for Elektron.se hardware machines but works with old samplers also!
I tested it with Yamaha A5000 and it works great! It uploads all selected samples one by one!
I’m sure that this utility will work with Akai, EMU or other hardware samplers.
This soft has Turbo Mode which can be set up to 8x.
You must experiment and find maximal value yourself because every sampler has own limit.
My Yamaha accepts maximal available speed Turbo X8 with delay 10ms.
Loading samples this way is still slow, but when you have to transfer short drum samples or just waveforms
this soft is very helpful. Upload 100kb wave to my yamaha sampler takes about 50 seconds.
Keep it mind that midi is prehistoric protocol :)
Update on 19 Dec: I just tested it with akai s3000xl and it works in Turbo x8 mode. It seems that this tool sends data to akai even faster than to yamaha a5000 because there is no significant delay after transfer is complete.