Bi-wiring means using separate runs of speaker cable to the HF and LF terminals on a loudspeaker. The intention is to gain some of the benefits of biamping (where each driver is driven by a separate amp) at substantially lower cost. There are two methods of biwiring from Cambridge amps.
The first is to connect both LF and HF runs of speaker cable to a single set of terminals on the amp and run them to their respective connections on the loudspeakers. With some of the smaller Cambridge Amps, this is the only option as they only have a single set of left and right terminals.
The other option is to connect one set of cables to speaker A and the other to speaker B and run them to their respective terminals on the speakers. This has the advantage that 4mm plug terminations can be used on the cables and it can often be easier to wire a single set of cables to each set of terminals. In all cases you will need to ensure that both speaker A and speaker B are selected.
The performance benefits of biwiring are not clear cut as the hundreds of pages of often vitriolic literature that has been written about it attests. Indeed many well regarded brands do not cater for biwiring at all and fit only a single set of terminals. Some speakers can benefit from a greater sense of separation and detail when biwired but equally some do not seem to benefit at all. If at all possible it would be wise to try biwiring out on a no hassle return basis before paying out for the extra cable.