I am making an assumption that OAX has the same setup as the OAA in OAS, but I would be surprised if it didn’t.
Bank 84 (In OAS) in the Sound list contained custom Wersi designed voices (Including Mega voice equivalents which had acc added at the end of the name) for Yamaha styles, and were used when a T2 style was loaded, (NOTE: the equivalent voices were only used if that type of sound was not available in the standard Wersi sound set) they were also used in Wersi styles designed for the OAA (.stw) including the revised factory styles. (Styles 2011)
Bank 84 was only available from the OAA style editor and was blocked from showing in other sound lists. (See if you can access Bank 84 in OAX as they should be the same as OAA in OAS)
NOTE: equivalent voices were only available for styles that were compatible with T1 & T2, which is why later styles T3-T5 will not load, as the correct voices are not available. (Style convertors to convert T3-T5 styles to the T2 format (It uses voice substitution) can be found here http://www.jososoft.dk/yamaha/
Hope this helps