MOTU Firewire driver - Measuring used (or available) Isochronous Bandwidth

I am looking at improving the Linux driver for an old MOTU interface 
(896 mk1), as the Windows driver supports disabling the ADAT 
input/output for the purpose of saving bandwidth. I think I have found 
the appropriate controls, but would like to confirm that these do 
in-fact save bandwidth.

Q. how can I measure the used (or alternatively available) bandwidth 
under Linux?

I believe that the different connections should have a peak bandwidth 
of:

4/6 pin - 400Mbps half duplex
9 pin - 800Mbps full duplex

Cheers,
Simon.