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Afraid not, wish I'd purchased two now! Yes it should attach to the other GXP BBs, I switch mine between Rival 22, S300 and soon a Rival 1 crank.
I think the Q factor is quite different with the Omniums, should all be in here.. https://www.sram.com/sites/default/files/techdocs/road_cranksets_fram_fit_specs_gen_0000000004165_rev_b.pdf
Crank / Q factor / difference for left side arm.
Stages Rival 22 - (Q 147mm )
Rival 1 (Q 149.6mm) 1.3mm
S300 (Q 145mm) 1mm
Omnium (Q 134.7mm) 6.1mm
How bad do you want power... I got a Stages Rival arm for £210 during last years black Friday sales. You could stick one of those or the 4iiii [probably] on the S300 [https://www.bike24.com/p229035.html] which basically uses a rival arm.