Sorry I missed the first part of this. I've got a 3400 sitting in front of
me with a similar config.

Yes the CXY08 is a serial MUX and NetBSD can talk to it just fine. 

The DSV11 is the point to point synchronous serial interface, that and a
CSU/DSU and you can talk to a T1 line. No I don't have docs for it.

The number '3' in the LED display means that the vax is sitting at the
Chevron prompt ('>>>') waiting for a command. Depending on whether you've
got the language switch set it is either waiting for you to tell it what
language to use or what device to boot from. 

The serial console connects through an MMJ connector, if you go to Tim
Shoppa's zShop on Amazon he will sell you an MMJ to PC serial port
connector that will let you connect the VAX serial console to your PC. Very
easy to use right out of the box.
<http://s1.amazon.com/exec/varzea/ts/browse-zshops/226861/002-4520159-1673850>

Once you get that connected you can ask the VAX things like how much memory
it has, what devices it can see, etc.

--Chuck