Some DBMs use a bifilar common-mode choke [which could be wound on a toroid] - and which may be described as a 'balun' on some ports ... it improves balance of the main toroid-driving-the-diode-quad.
If this is the case I'd be expecting two of the toroids to have three windings (the ones connected direct to the diodes as in the classic DBM input/output circuit) and two of the toroids to have only two windings.
As an example see fig.10 here:
http://www.robkalmeijer.nl/techniek/...991/04/page39/
where L6 and L8 are the common-mode chokes.
There are other possible 'networks' you could find in these things for impedance-matching/power-division/combination.
As to which is the input and which is the output - it may well be symmetrical!