I dumped the EPROMs for the Wersi MK-1/EX20 cartridges that I have (ROM 1, ROM 2, ROM 6). These all contain 27128 16Ki x 8 EPROMs. Two of them were socketed, but the clearance inside the cartridge was very tight. Wersi used low profile sockets and trimmed the pins of the EPROMs so that they would fit. I added a socket to the third one, but it was difficult to reassemble. If you have a cartridge, you should be able to burn new EPROMs and swap them out.

The most notable sound here is the CHOIR patch from ROM 1. There are 5 different formant waveforms that cycle between different vowels (a, ɛ, i, o, u) with each keypress. You can edit the sound and reprogram each of the waveforms (the formant effect is lost but the cycling remains; I used that effect here). But saving the sound to a user preset loses the cycling effect.

ROM 1 dump
ROM 1 sounds:
MARIMB
A-PNO1
STAGE2
S-HARP
XYLOPH
CELEST
CHOIR
K-BASS
EGUIT1
SYN2
BRASS3
BRASS4
S-BRAS
TROMB1
TRUMP1
STRIN3
TAKEOF
S-DRUM
HEULER
LASER

ROM 2 dump
ROM 2 sounds:
SYN 10
SYN 11
STAGE3
CLAVIN
SYN 12
HARFE1
SYN 13
SYN 14
SYN 15
SYN 16
BRAS10
BRAS11
SYNSAX
SYN 17
SYN 18
SYN 19
SYN 20
AKKORD
STEEL1
SYN 21

ROM 6 dump
ROM 6 sounds:
US-ORG
US-GRD
US-STG
US-PNO
MELLO
E-HARP
SAM=BS
SLAPBS
DETUNE
STEVIE
PHENIX
OBELIX
JARRE
HUMAN
ACCGIT
DREAM
SAMPLE
PIPES1
BELLS
SQSOLO