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The other way to go that would get you a single set of filters to share between the two cameras would be two series adapters--37mm SO to Series VI and 40.5mm screw to Series VI and a single set of Series VI filters.
I know this doesn't let you use the filters you already have on both cameras but may be a slightly simpler way to go.
A quick search on ebay turned up this:
http://cgi.ebay.com/Series-VI-6-Adapter-Step-Rings-Filter-Holder_W0QQitemZ130357576157QQcmdZViewItemQQptZLens_Accessories?hash=item1e59eac1dd
I've never dealt with this seller but they may have the appropriate adapters for your cameras. Once again, I'd email and ask.
Good luck!
Rob