You may download stock ROM in .ftf format and flash it using FlashTool (search for any B.Jay's post and look at his signature - there's a link to mediafire folder). And I'm a little bit surprise that SEUS doesn't recognize Your mobile, cause You pick it by yourself. Maybe You're talking about Pc Companion?
Anyway - this problem is popular so I'm sure You will find the answer.
Xperia X8 black +
Xperia mini pro black +
nAa 18.104.22.168 kernel +
JellyVanilla 7.1 +
16GB Sandisk Ultra class10 microSDHC +
Panasonic RP-HJE120 ergofit