Hi 
- thanks for the tips - just as you thought - it’s all becoming a bit clearer. There seems to be a lack of documentation from SL (on Cubase setup) on this i.e. not very comprehensive, so this post might be useful for others to ask similar questions on the SL Mixface device, as I am sure I will 
.
In this case it was just a matter of disabling various inputs in CB Setup - my midi-ins bypass this device but I hope to run an SL73 or similar through it to take full advantage.
Many thanks for the help roja
Colin
(Lowtech)