I just bought a blackstar ht-5 head and I also have 2 external cabs wich are both 8 ohms. My idea was to hook up both cabs, until I read this:

The output marked ‘1x16 Ohm’ is for the connection of a single 16 Ohm extension speaker cabinet (or the internal loudspeaker of the HT-5 combo). The outputs marked ‘1x8 Ohm or 2x16 Ohm’ are for the connection of either a single 8 Ohm extension cabinet or two 16 Ohm cabinets. Also, the internal loudspeaker of the HT-5 combo can be plugged in here if it is used with a 16 Ohm extension cabinet.
WARNING: The output marked ‘1x16 Ohm’ should never be used at the same time as either of the outputs marked ‘1x8 Ohm or 2x16 Ohm’.

here's a picture: http://www.thomann.de/be/prod_bdb_AR_216097.html?image=5

so does anyone know a safe way to make it possible of hooking up both cabs?

You can only match them by wiring your cabs in series into the single 16 ohm socket on your head. Since there aren't many cabs that support series operation and I'm betting you don't have one, the only other option is to change the wiring in the cabs. Exactly what cabs are they?
thx allready

well, cabs:
1 cab is a 1x12 100Watt 8ohm from the German webstore Thomann, speaker is blank so probably homemade
the other cab is another thing; it's not a cab yet I got this 10 year old peavey bandit from wich the amplifier itself is totally f*cked so I thought instead of trowing the whole thing away; why not make a cab out of it? there's only one catch here; there's no writings on the speaker and I keep finding different information. In an old Peavey-catalog it says it's a sheffield speaker 75W and 8ohm, but on the net I can only find that speaker with 16ohm....

I still think it's 8 ohm but if anyone can help me with this, please let me know. certainly dont want to blow something up!

allright, thx

could anyone guide me through this? or redirect me to another topic/forum/site?