i think the adapter you need is a Shure WA 310 http://www.thomann.de/de/shure_wa310_anschlusskabel.htm.
With this adapter you can attach a standard dynamic XLR micro (e.g. SM58) to the Line6 XD-V Beltpack with TA4F TQG.
(I assume in your application the AKG B29L male XLR-out acts electronically as a standard XLR Mic)
Unfortunately this adapter is 29 Euro at Thomann.de shop, but if do-it-your-own soldering is an option for you
- Switchcraft TA4F TQG http://www.thomann.de/de/switchcraft_swcta4f.htm
- Neutrik female XLR http://www.thomann.de/de/neutrik_nc_3_fxxb.htm
- decent XLR cable like http://www.thomann.de/de/sommer_cable_primus_sw.htm
- Shure WA310 wiring pinout http://shure.custhelp.com/app/answers/detail/a_id/1498/~/pinout-for-wa310
As i understand the AKG B29L is a 'mini mixer' for two AKG specific clip-on mics, so i think the XD-V75 TR is the better option for you.
The Relay G90 is for guitar players and offers guitar-specific options like 'guitar cable simulation' ...