Topic: Can record my synth but always seem to be monitoring the master out?

Hi, I have a hammerfall 9632 + 2 expansion boards. 

I have plugged my synth into ADAT 1/2 and the speakers are attached to Analogue 1+2

What I can't seem to do is to put (e.g.) a hi pass filter on the input channel in cubase (ADAT 1/2) and sweep it to affect the sound being recorded by Cubase. I am pretty sure the routing is set up in correctly in cubase:  the audio track I record onto receives the audio, but as I tweak the hi-pass filter on the input there is no effect to the sound coming out of the speakers.

People tell me that I must be monitoring the inputs to the soundcard rather than the outputs, is there something I should disable in Total Mix?

Thanks!