It's true. Previous versions of System Software(4.46.1, 4.50) on DEX have stopped getting access to PSN. You'll need a spoofer to continue on PSN.
Use REBUG 4.46.1 then install this .pkg file over it. Set CFW to "REBUG Mode" and you should be fine.
Link:
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There is a spoofer for PS3ITA but it's a bit more complicated and doesn't come in a .pkg file, so you're on your own.
I suggest looking here for that solution:
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