For those of you interested in delay and IEM's here's a study done by a group of Shure guy's in 2007. I gives some interesting insight as to who is affected more by delay. You need to get past the first half of the paper on measuring conditions etc. and get to the meat of the matter. Happy reading.
http://www.lsbaudio.com/publications/AES_Latency.pdfAs to wired directly off the aux outputs, it may work but leaves a lot to be desired in the sound quality dept. The Behringer P1 may be just the ticket for this application or you could spend a little more and go for this guy's design. You can DIY or buy the assembled unit. For the techies out there it gives all that you ever wanted to know about earphone amp design. His input needs to modded for balanced line in for use with the DL.
http://nwavguy.blogspot.com/2011/07/o2-headphone-amp.htmlIf you want to bypass the EE part and get to more audio oriented explanation with lots of real world examples then try this article.
http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.htmlSo after reading this I went back to the DL spec on outputs and for some reason I had 50 ohms for the aux's in mind well what a surprise a mere 240/120 ohms on aux's and and even worst spec on L/R of 600 ohms. So much for the 1/8 rule for head-amps that would put 960 ohms for the headphones or earplugs (unbalanced). Good luck finding those. If you actually believe that the aux's sound good direct keep on playing! Great job Mackie for cutting all the corners. No specs on their headphone out plug. I wonder why?
The Behringer P1 is specked at 10 ohms not so great but way better than aux's.