I don't know the roland pc-180, but just in case, most roland keyboards have 2 midi out's and two midi ins.
In that case there's no problem, but I guess seeing your post the pc-180 has only one midi out and one midi in.
And I assume you don't have a midi-patchbay.
This means your midi signals can only go to one receiving slave device, which slave device will have to transfer the midi signal "thru" to another slave device.
As your two slave devices are computers with soundcards, only the latency alone will make it almost impossible to work in realtime.
Secondly your software should support sending midi-out to more as one device.
(sampler software + midi-out for midi thru signals to other soundcard -> midi in->software cubase.
This routing can be achieved by installing hubi's midi software on the pc where your sampler software is.
Once achieved you need to make sure cubase is not sending mid-out again as you create a midi-loop.


The easyist and most wanted way is using a midi-patchbay.
No latency problems
Easy routing

You can ofcourse try out first, as the hubi software is free for download (it's freeware) but I doubt or it will work without latency problems.

Fred

Note:
I don't have the link for hubi on hand, but I'm sure that with one google search you will find it.