Sorry but Cisco IPS and CX modules cannot both be active on an ASA 5500-X series appliance at this time. You need to either use external IPS or web security with the other feature on the 5500-X.
Options include:
- Cisco (or other vendor) IPS appliance plus CX, or
- external web security from Cisco (WSA or cloud-based options) or other vendor (Bluecoat, etc.).
CX is pretty new and is a bit early to jump on it right now in my personal opinion. WSA is quite mature. Cisco IPS has been getting lesser market share in favor of Sourcefire (acquisition by Cisco pending), McAfee and other competitive vendors.