I have the chance to purchase an An1x. I was wondering if I should get the An1x, or if the later CS2x is better? Also, does the EX5 incorporate all of the features of both the above synths?

well the CS2X offers you a lot of dance sounds and the AN1X anologue modeling
they are very different check out the YAMAHA webpage

I have an AN1x and I researched the EX5. The CS2X has some of the ROM sounds that are in the EX5. The AN1x has 10 virtual analog voices. The EX5 has 2 virtual analog voices, so it really doesn't "include" the functionality of the AN1x. Two new synths that kind of do are the CS6X and the S80, if you buy the analog modelling daughterboard. It gives you 5 voices (still not ten, but enough for a pad. BTW, I am very happy with my AN1x. It can be big, bold nasty, wispy, warm, cold, glassy, whatever. It has some lovely sounds.