Testing transducer

[Albin32TE]

New raymarine user here.
I have a A128 in my new to me Albin32TE, with a Cpt100 on the transom, and what I think is a B60 mounted as a thru hull. The B60 is mounted near the keel, about 4’ from the transom. The B60 is not connected and the cable is just coiled up below the helm. The cpt100 works great until I’m at 10 knots, then too much interference/lack of clean water.
I tried connecting the B60 to the A128 with an A series-HSB2 cable, but it didn’t really fit into the back of the mfd. it was too tight and not sure if it was making contact as I couldn’t get it all the way in. I thought it was in far enough, but couldn’t get the mfd to detect it. It was either bad to start, or my cable wasn’t connected. Is there a way to test the transducer with out connecting it to the mfd?
What is the best transducer that will work with my MFD? Saltwater salmon, halibut, tuna on a 20 knot max boat.
If I purchase a CP370, does that allow multiple transducers? One plugged into the mfd, and one via the cp370?

Thanks,
Eric