Digital BW, The Print

Reading through Clayton's excellent pages re. BO and general B/W 
printing, my old "art" printing memories came back! :) But since we 
are in the 21st Century, and using this i950 printer, I was wondering 
and need some clarifications on this BO process:
- as I understand BO stands for using ONLY the black ink cartridge 
for printing grayscale images
- if this is true, than what happens with the rest of the inks, you 
simply take the out? I guess that could imply some problems with the 
printer itself.
- or, you can replace the remaining 5 slots with empty carts 
and "force" print in BO only?
- as far as I know, even in grayscale printing normally used for 
text, the "black" ink on paper is not 100% black, but a combination 
of black and other, thus resulting in a color tinted B/W photo print 
straight out of the application.
- since I guess is possible to replace the whole printing head in 
this printer, would it be advisable to have a separate head only for 
the B/W printing? If such, where or how can you find an extra head 
since I don't think Canon is selling these separately?

Any input would be greatly appreciated. I looked into the archives 
for the past year and more, couldn't find any specific info on this 
printer model. I understand people here are more Epson geared, but 
even some general info re. my issues above would be helpful.

Thanks,
Ara Ghemigian