Rob:
The Xantrex C60 controller is a low frequency ( about 100 Hz as I understand it) using a small microprocessor to limit the current to 60 amps and as well to detect the voltages of interest.
It seems that the schematic, you are showing, ( too dim and missing connections )is from one circuit offered by Home Power if it is such, reply to me directly and include the schematic, the tell me the solar panel total voltage a peak sun as well as the current capacity of the solar panels.
With this info I may be able to tell you what type of circuit changes you need to do to work with your friend's system.
A better design would be a PWM charger controller like the ones made by OUTBACK Company that operate about 30 KHZ and do a much better job.
Regards
Nando
nado37 at comcast dot net