DECServer 90L+ startup help

I have a pair (3 actually) of the above terminal servers - I have them cabled up, yet the two I have connected seem not to play well together... the remote terminal (a VT220) displays : The other unit is connected to a port on my 11/44, also known good, tested and working locally to the machine. The first two green leds are on , the led next to the MMJ ports flashes when I transmit data, but the '#' light remains, sadly, dark. I have used a couple of known-good 50 ohm BNC cables between them, tried powering them down and up while connected - no joy. I have Googled mightily - found a bunch for sale, lots of references to them, quite a bit of really esoteric data - but no "User Manual" yet - save for the pointer to one on a now defunct Compaq site. So I'm wondering if anyone with some experience with these little beasties could afford me a clue or two? All I want is a pair, one in the "Machine Room", one in my office, and a cable (or wireless setup) between them. Thanks In Advance! Cheers John