Dave Smith Instruments SYNTHESIZERS

I am trying to 'properly' set up my system with MIDI - it kind of worked before but on trying to add the Tetra using a MIDI merge I set up some nasty MIDI feedback and realised that it was more luck than judgment that had made it work before...

So back to basics...

1. Picked a combo sound - latch it to keep playing with "Push me" - and listened to dramatic effect of playing with Cutoff / Resonance

2. On my Tetra I set the following global parameters (just showing what I think are relevant):
MIDI Channel = 4
MIDI Parameter Send = NRPN
MIDI Parameter Receive = All
MIDI Control = On
MIDI Sysex = On
MIDI Out Select = Out
Multi Mode = Off
Local Control = Off

3. Now my theorey was that when I routed the MIDI through my MIDI interface (Remote SL) the controls on the front of the Tetra should effect the sound coming out of the Tetra (I had initially set a sound going) BUT they do not (I latched a Combo going before switching local off). 

4. So my next step was eliminate other routing (the Remote SL) and just hook a MIDI cable between In and Out Port of Tetra - again tweaking the Cutoff / Resonance had no effect on sound (however there seemed to be some 'feedback' coming into the pot as it was not always reaching its full numerical value. 


Why is this not doing what I expect - is my expectation wrong or is there something in the settings I should be doing differently???

Many thanks in advance for humouring me!