Just one thing first. No offence but, I wouldn't create a new thread as a follow up, it makes it very difficult to keep track of what has been said for others to follow on a given topic. Just keep replying to the same thread!
First of all a word of warning. Do not under any circumstances take an output feed of the Quantum or 192 (I now use the Quantum) in to the line input of the drum module! It won't damage it, but I made this mistake and when you hit monitor on a track when listening via the headphones of the audio device, you get a extremely painful shriek as you hit an audio loop. I had this bright idea of doing this a while ago, so I could hear Studio One when monitoring in the TD15 module whilst playing the drums. I would then go to my S1 on my desk, put another set of cans on and then click on monitor for a track and Shreiiik! After thinking about this I worked out why and realised it was a good old fashioned audio loop.
So the answer to your question is I always monitor on the Quantum. I have headphones 1 on my desk and have fed an extension from headphones 2 to the frame of the TD15 so I can plug in whilst playing drums. I also have an iPad fitted on the TD15 frame so I can control the transport of S1 for playback, record, rewind etc.