the C426Be is not an option due to cost and the C208 is too big and ugly
C426Be dismissed due to cost, yet it's bigger than the C208 which was dismissed because it's too big?
What dimension and cost limitations are your requirements constrained by? Will the centre be used with subwoofers and bass management?
Agreed, it's not ideal, but you've already entered less than ideal territory once 3 matching speakers weren't deployed with each tweeter at ear level, so now you just have to decide
which compromise you want to make.
what the other options are
Sticking with Revel, you could deploy one of their in-wall architectural speakers, if your setup would allow for that.
Another option would be to borrow a random manufacturer's $500-1200** centre channel from a friend to see if you actually enjoy it when used with your $7000 Revels.
**(range pulled from the Infinity and Kef you're considering)