Instead of using the auth_header.authtypecode as the authoritative authority entry type look at the 008 position 14-16.

According to MARC standards ( https://www.loc.gov/marc/authority/ad008.html ):

* 088 position 14 = 'a' means the authority record is a name authority
* 008 position 15 = 'a' means the authority record is a subject authority
* 008 position 16 = 'a' means the authority record is a series authority

These three characters allow authority records to belong to multiple auth types. Koha only allows an authority record to have one auth type. 

Given a syspref is enabled load all authorities into the default authority type. Search/use/display them according to how they are coded in their 008 positions 14-16