1. when Data Transferring from 3.55 to 3.66 or Vice Versa, you'll need to disconnect your PS3 from online whether it is wired connection or wireless.
2. Plug in your Ethernet cable to both ps3s(i heard it's a lot better if you put them in separate rooms), also making sure that you're still not connected to the internet.
3. not entirely sure if you need to have spoofer for 3.55 to receive, but just to save the trouble I think you should get a spoof, CFW rebug, because you're going to send it right back anyways.
4. Data Transfer the 3.66, which should contain the patch, to the 3.55 ps3. it should work.
5. then use blackbox FTP-File Zilla(or any other program comfortable for you) to transfer the patch_mp.ff over.
6. this time, you Data Transfer 3.55(using rebug spoofer or any other compatible spoofer) to 3.66 FW PS3.
this should be a success:y:

**If oit says you're Ethernet cable is disconnected or it doesn't seem to begin Data Transferring, then you should try the Crossover Ethernet cable because it worked for

Hopefully i helped.

It also helps alot if u delete some user on both ps3's so that the data transfer doesn't take forever, and once a patch is on your 3.66 u should save your ps3 datato a usb so that instead of re-data transferring the same patches over and over u can just load them from the usb.

I'm not sure if Users will matter much depending on what saves/data you have but Definitely delete the Game Data stuff(not ave game), excluding the one you are going to put the patch in.
plus I don't think it's possible to just Copy the patch over via USB,/facepalm if that's what you meant.