My understanding is that the x1700 and x2700 both have the same Audyssey MultEQ XT.
The x3700 and upwards have XT32 with Sub EQ HT.
The S series models only have the MultEQ. (Note, not XT).
In which case what extras are you getting with the x2700 to justify spending extra and getting a bit less future proofing hdmi wise