Most headsets that are intended for wireless will work.  The issue is a combination of how sensitive the mic is and how loud the performer is.  So a mic that may not work for one person may work great for another.

Previous to V2.x firmware, the output of all Line 6 wireless systems was unity compared to the input.  In other words the mics acted just as they would if they were "wired" versions.  Running at "unity" is still sonically superior but V2.x firmware (used with V70/75) added an output level control that can boost level by 12 dB or cut by 18 dB.  This does make it more versitile.