Some links me & my friends find useful and use as a reference!
Retrokits RK-002
Updating my RK-002 Cable from Retrokits which I use to have aftertouch and velocity sensitivity on my Volca FM
Uploading new sysex files to my Volca FM via the following link:
Checking my cables connectity and uploading new firmware apps:
Updating the firmware to other versions for other synths:
Directly editing the settins of the RK-002 for the Volca FM:

Synthforum.nl
Thé (Dutch) forum for Synthesizer-lovers!
Discuss, browse, listen or talk about synthesiZers, all carefully maintained by the (volunteer) moderators!
Synthesizer Basics Explained
This link is very useful for when you are starting with Synths or starting towards (semi-)modular such as the Behringer Neutron. I used it to understand the flow in the Neutron and in combination with the manual then decided to visualise this flow on my Neutron front.
https://www.sweetwater.com/insync/synthesizer-basics-explained-with-audio-samples/