The 6100 is rapidly becoming impossible to drive - it's already incompatible with the newest couple of MacOS releases, and Canon will almost certainly not update the drivers the next time Microsoft changes Windows printing (it does work with current Windows)... It uses two ~$450 heads, which tend to fail together - if you're facing one head replacement, you'll probably lose the other in a few months (if not while changing the first one, which stresses the remaining head).
Time for a new printer... One good option is the great-great grandchild of your printer, the (relatively new) Canon Pro-2000. It has improved gamut across the whole range of colors, while retaining Canon's special strength in the blues. It's faster, and quite a bit easier to feed paper to. It retains the wonderful Canon feature that it doesn't care how often it's used - you can let it sit for months, then run 25 prints in a day, or you can run prints every day (Epsons get mad at you if you don't use them enough).. It's not quite as long from end to end as the old 6100 (the inks sit essentially above the paper instead of off to the side), but it's substantially heavier and bulkier. That increased bulk means that the pieces that felt a bit flimsy on the 6100 no longer do - although the paper catcher still comes unhooked on occasion... It no longer uses two heads - the one head is somewhere in the $500-$600 range, which is much more palatable than a double head replacement on the old machines. The bulk also means that you have quite a bit of choice in ink sizes - you can use 160ml, 330ml and 700 ml cartridges. It's a great machine, and not especially expensive (right now, you can get them for a little over $2000 before a $300 mail in rebate - Shades of Paper generally has good pricing on Canon printers). The $2000 printer comes with a $500 head and $1200 worth of ink (essentially, you buy a head and a full set of inks, and you get a 200 lb printer for free...).
