Head+Cab+Combo?

Ok as I've posted before I am looking into buying the GK Backline 250 Head along with a 2x10 and 1x15 backline cabs. The thing is I want get it asap however to do that I won't be able to purchase the 1x15 so what I was wondering is if I could use my carvin PB100-15 in the meantime. In the back of it I noticed the head built it plugs into what must be the cab built in. So could I just unplug the chord and have a chord from the GK Backline head to the Carvin built in cab? I hope this is making sense.