Using Plantronics RIG mixer as a DAC/AMP for mic loopback

[Prince Churming]

Hey, i'm currently in the market for a new pair of gaming headphones, and have decided to go down the separate headphones and mic route.

i would be looking at a pair of DT 990's with a ModMic 4/5.

my main problem however is that i would really like to keep the mic loop-back feature that my current Plantronics RIG headset has.

 

my plan is to get an adaptor like this http://www.misco.co.uk/product/198034?affiliate=GOOGLEPLA&cm_mmc=google-_-Product_PlusBox-_--_-198034&gclid=Cj0KEQjw4cLKBRCZmNTvyovvj-4BEiQAl_sgQmjPkGFr3g-0y01R7DlP0R_wtLjXoSdTP2CssNz2tDIaAnGS8P8HAQ and plug both the dt990 and the modmic into the headset port on the RIG to provide the same loop back. I believe that the RIG mixer acts like a DAC because the output from the pc is a USB (digital) and the output is 3.5mm 4pin (analogue) and to my knowledge is also a AMP due to the ability to change the volume. I've done quite a lot of online research into using the RIG mixer as a DAC/AMP that would also allow for hardware mic loop-back but found almost nothing. 

would this work, and if so, approximately how much quality would i sacrifice by doing this. also that would be the best OMH resistance to buy the dt990's in for such a setup.

 

many thanks