We can always try home based DBTs. Just make sure the volume is matched within 0.1 db (so you need a very accurate SPL meter) or within 0.01 volts (so you need a DMM) and it is double blind, so the person making the changes is different from the person conducting the test who is of course different from the subject. So at the minimum we need n+2 people, where n is the number of subjects.
-akhilesh