I used the original plugs with different wires on my system. I did not find out whether the plugs can be purchased - and I wanted to use my already installed (good) speaker wires:

- pull the metal plugs out of the plastic ends (use pliers on both the cable and the plastic end to prevent cutting your fingers with the metal plugs)

- cut the original wire and solder yours to the metal plugs (keep it small - the plastic ends are quite narrow). alternatively you could leave a few blank millimeters of the original wire to ease soldering (wire to wire), but then you will have to isolate the blank wires

- re-insert the metal plugs into the plastic ends (preserve polarity).

not the funniest job, but it can be done.

I dont know whether this voids your warranty - which you might need (see firmware thread...)