Major delays on group channel using Cubase 7.5

Hi there,

I have the following routing setup:

Thesys (MIDI step sequencer) --> Massive (Synth) --> Group Channel (Inserts: 1. Multiband compressor; 2. Vintage Warmer; 3. Compressor side-chain). Both thesys and massive are each on an instrument track.

The sound is out of sync compared with the rest of the project, while constrain delay compensation seems to remedy the problem with the effect that I can’t use the inserts on my bus. If I route it straight to stereo out it’s alright if no inserts are inserted.

I have to confess I am using an oboard soundcard at the moment but wouldn’t have thought that the delay is due to that as no signal really exits the box.

What can I do to improve this?

Thanks so much in advance.