a number of points need to be investigated before you attempt to connect further speakers to this or any other combo. 1."ohms" rating is normally given as a minimum figure, this means that the total ohm rating of speakers connected must not go below the rating on the back panel. 2. the "ohm" rating of a speaker is the measure of its resistance to any signal that is put into it. if you look at each of the speakers in the back of your cab you will see that each speaker is probably rated at 8ohms and that these speakers are wired together in parallel- ths means that if one speaker blows, the other will still work as the spkrs are not connected in a simple loop,instead each speaker can be seen to have a "+"/red wire and a "-"/black wire which go back to the output stage of the amp, think of it in this way- the spkrs run side-by-side not one after the other. if spkrs are connected in parallel, the sum rating will generally be half the ohm rating of the individual spkr – two 8ohm spkrs connected in parallel gives a total rating of 4ohms. if your spkrs are 8ohm each and the amp will run down to 4 ohms your are already on its lower limit and therefore you must not connect any other spkrs in parallel as this will probably result in a blown amp. The best thing to do if you want to tackle this job (if you are not familiar with spkr configuration)is maybe to seek advice from a friendly local music shop or an experienced musician or check out various sites on the net. if you want an easy way of running both combos together why not try this:- if the Duece has a line out socket-(DO NOT USE SPKR OUTPUT FOR THIS METHOD) then you could connect this to the guitar input of the Cambridge. start off with all master volumes down to zero, then get the sound you like on the peavey then slowly turn up the volume of the vox to see how much extra sound and spread this will give you – this can work well when gigging with one amp each side of the drummer best of luck jack