For me, the best way to interface with my DEC hardware
was with a (hardware) TCP <> LAT converter.
Xyplex made one many years ago (The MaxServer 1710)
supposedly supported 24 concurrent sessions.
I have one, but I've never used it, due to lack of
documentation on the product.
Instead, I rolled my own version using
Micom's Marathon series of Integration Multiplexors.
Using either a Marathon 2K, 5K, 5KT Pro, 10K, or 20K unit,
combined with their "Remote Terminal Server" option module,
you can create a TELNET <> LAT server, which will allow in excess
of 32 simultaneous sessions.
I can't provide any throughput statistics, however it should
handle anything that a (real) PDP-11 could throw at it.
The base units can be had off of e-bay for $25 - 50, and are readily available.
The Remote Terminal Server module is a bit harder to find;
I've seen them for $45 - $125 over the years.
You can still get them NEW for about $250 from the Marathon Store,
though this price is several years out of date.
At any rate, you can't get much more universal than TELNET. ;-)
My equipment is currently in mothballs right now,
but if anyone is interested in the configuration settings
required to make the Marathon equipment work,
let me know, and I'll dig up the info.
T