Among the MBHA’s goals is to provide learning materials for those interested in pursuing singing, arranging, or coaching in the mixed-barbershop arena. This document collection will grow over time, let us know if you have anything to contribute here!
Here’s an article from Brian Beck on Arranging for mixed voices.
What key is this song in? by Dale Summer
Who Sings Which Part – a Mixed Barbershop Quartet FAQ
The MBHA is carrying forward an effort and vision championed by Kim and Jerry Orloff, see their Legacy MHBQA website for lots of other articles and history.