Wonder if this would be a good alternative to the M jack for certain dynamic driver IEMs? http://ifi-audio.com/portfolio-view/accessory-iematch/
Yep, this is good, and probably better than the M Jack in terms of built quality and functionality. This is good for ultra sensitive IEMs and very useful for flights (especially for loud announcements which max out the volume).
However, it adds bulk and I think it will still affect SQ.
For the Calyx M, most of the IEMs will not require the M jack. Probably only those ultra sensitive ones (none of my IEMs in my collection requires the M jack).