Have been running El Cap in various environments since the betas. The primary issue in my view - for all applications and in particular re. licensing - is that ElCap has dramatically changed its security features, including no permissions rebuild via Disk Utility, the introduction of SIP (System Integrity Protection) and the removal of the root account. Google that. The Steinberg stuff runs fine on the face of it, but all sorts of problems can arise with 3rd party apps, plugs, VIs, utilities etc depending on how the authorisation scheme works. Am working with a US developer on that problem right now. Otherwise, I find that El Cap does a much improved job of working with the VDUs & GPUs, and especially if the work includes say PhotoShop or various Video NLEs.