Haha, great!!! Now I want to see you adding two on top of the MDD cage.
If you like to add cheap SATA to it and do not need boot-capability (would give you thinner cables

and with PCI-X 62MB/s) I have this one
http://www.ebay.de/itm/SATA-Raidcon...29VmEqUkgNqZcwFsZ3vIc%3D&orig_cvip=true&rt=nc
You only have to install the SIL3124 drivers. Either way you keep on watching out for it cheaper or take this
http://www.ebay.com/itm/PCI-X-SIL31...sk_Controllers_RAID_Cards&hash=item27da470487 (don't know about taxes from Canada to US, though).
I also saw that the US ebay has a lot of these flashable wiebetech cards. Also there are Addonics cards which are said to be very similar to the Sonnet cards and are said to be working, too, out of the box.
This one has 8! SATA ports and is compatible out of the box from 10.4.9 on (no boot)
http://www.ebay.com/itm/8-PORT-ESAT...sk_Controllers_RAID_Cards&hash=item1e88dd2514 (though a bit costly)
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For better price value search for
AMCC or 3ware or LSI and PCI-X you get results for 14,-USD and 4 to 12 ports. You have to check which ones are compatible on their homepage, though. I do not know right out of my head (I had found them a while ago).
Edit: ah, found something different, but suitable "Official support for 9750 (3DM2/CLI can be used with all 7000/8000/95xx/96xx controllers)"
http://mycusthelp.info/LSI/_cs/AnswerDetail.aspx?sSessionID=&aid=8262 (search the site for Mac in your browser.)
I wonder if this one for 9,99USD works
http://www.ebay.com/itm/3Ware-Escal...sk_Controllers_RAID_Cards&hash=item3f3130d1c7 (since they say all 8000 cards, but maybe they consider it as 85xx).
Edit2: here it says only the 96xx and 97xx cards with PCIe (which would be the last G5s) are compatibel
http://mycusthelp.info/LSI/_cs/AnswerDetail.aspx?sSessionID=801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[&inc=8261&caller=~%2fFindAnswers.aspx%3ftxtCriteria%3d9650SE%26sSessionid%3d801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[
But then again their is a "CLI guide" for Mac for the 95xx cards here:
http://mycusthelp.info/LSI/_cs/AnswerDetail.aspx?sSessionID=801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[&inc=7270&caller=~%2fFindAnswers.aspx%3ftxtCriteria%3d9650SE%26sSessionid%3d801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[
Addendum for 96xx cards for Mac
http://mycusthelp.info/LSI/_cs/AnswerDetail.aspx?sSessionID=801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[&inc=7292&caller=~%2fFindAnswers.aspx%3ftxtCriteria%3d9650SE%26sSessionid%3d801441007OTSZRCXIUXMKNYPWVSWPSFFMMUSJNH[
Or this for 4USD, if they stated the exact model number
http://www.ebay.com/itm/LSI-Logic-6...rnal_Port_Expansion_Cards&hash=item3cde602c96
Hehe, or 3 4port cards for 60,-USD
http://www.ebay.com/itm/Lot-of-3-3W...sk_Controllers_RAID_Cards&hash=item565c03817f
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This
http://www.ebay.com/itm/Silicon-Ima...sk_Controllers_RAID_Cards&hash=item3f320752b3 card looks like it would run with the SIL3124 drivers I am using with the purple card I posted at the top. No guarantee, though.
There are supermicro PCI-X cards that share chips with the 3ware cards and you might also do a reasearch on Adaptec and Highpoint PCI-X cards.