To me, it sounds as if most of the VH units, including some of the built in systems, are more suited toward a female voice. And, unless you have UD's right hand ability to control the harmonies, they tend not to be very full and natural. Of course, like anything else, there are exceptions to this, some of which have been posted on this site and others.
All the best,
PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!