If you put the race to dwarf you can get +10 from Dex with the three dwarven race enhances.
The limiting factor appears to be the shield, with Cavalry plate and the two Dex releases from the Defender line and three releases from the Fighter and Dwarf enhancements each, you could have up to 11 Dex off the plate.
Unfortunately, with a normal mithral shield I can only get 10 from the tower shield. If there is a shield with one more dex allowed on it, then you could achieve a total of 11 from Dex max I believe, just don't know what shield that would be and still be a tower.
EDIT: Ah, you're talking Syberis not Stalwart, so pally. Sorry, not helpful I reckon. Although if you did go Dwarf, you could still raise your dex from 7 to 10 allowed on the armor.