As credentialz said... the only way you can downgrade an OFW greater than 3.55 is with a Hardware Flasher ... and even with one, there are some models that cannot be downgraded.
The worst part is that you cannot install any of the emulators available, in fact, any hombrew application, on your FW.
One route is to try to find someone that has a Hardware Flasher and knows how to use it to get him/her to downgrade your unit. Other route would be getting a Hardware Flasher yourself and become that one that knows how to use it.
And another one would be sit patiently and wait to see if th PS3 scene hackers get access to the keys that will let any PS3 to be jailbreaked, no matter what its FW is. There has been rumours about this getting real in the near future... but... Cheers! .. and good luck!
Just checked on this very site .. and found this: http://www.ps3news.com/forums/ps3-ma...tml#post446286
Maybe it's the answer to your problem!