Mostly true, while VST System Link does require a Steinberg product installed on each computer (Cubase, Nuendo, etc) and an audio interface with a digital audio connections on each to work, running In/Out from computer to computer, or daisy-chaining from machine to machine in the network in what they call a ‘ring network’ … to be clear, the VST System Link data & audio can very well be ran through the same digital cable without issue.
The problems Steinberg notes themselves is, only when you have a LOT of midi information passing through the digital audio cable, along with several audio tracks. This can be resolved by, #1 simply running data & audio via separate cables, or #2 running it via say, an 8 channel adat cable, using 1 channel for data only, and the other 7 channels available for audio, #3 simply record all your midi into a dedicated VSTi mamchine in the network, eliminating the need to send midi between machines in the 1st place.
I don’t know how many machines you’d have to be using within a VSL network to make this necessary (maybe 4 or more computers), but if total latency becomes too much of an issue, you can have one ‘main mix machine’ as your ‘master’ for accepting all other machines audio signals, this way all the audio signals arrive at the same latency. Same with using a dedicated sync machine.
I’m sure either works very well, but is a matter of preference & one’s own needs of course. I personally like the idea of syncing separate DAW machines together for the most flexibility…whether that be by VSL, or a dedicated sync device. Again, if VEP is also able to function as a full-featured DAW itself, then VEP would be the king of flexibility at a reasonable price point, but I don’t believe this to be the case.
I also don’t subscribe to needing another audio interface in general as being an issue. I’ve bought several full fledged audio interfaces fairly cheaply. Even when I was doing old school audio/mid networking a few years ago, it was only ‘one midi cable’ (from Master) and ‘one audio cable’ (back from Slave).
As for the OP, I’m still not clear why anyone would want to invest in both, I’d say one or the other. Even if it’s possible to ‘use’ both simultaneously…and it may be, it would get complicate fast.
Besides my original assumption of the OP wanting to use both methods simultaneously, as was each designed for… one thing I was wondering where he was going with this, if he was considering the possibility of sending VST System Link via Ethernet? or visa-versa… the possibility of send Vienna Ensemble Pro via a digital audio connection…??? I’d question if this is even possible(?)