Ward, thanks for highlighting the CentOS 6.7 problem. It wasn't actually a CentOS 6.7 problem, just something with the packaging that caused sipxopenfire to not install. If you 'yum install sipxopenfire' this fixes the older RPM installation. Also for a regular 'yum install sipxcom' that should be sorted now. The system works fine on CentOS 6.7.
15.08 was just released:
http://wiki.sipxcom.org/display/sipXcom/sipXcom+15.08
As far as memory use / kitchen sink arguments, I hear ya. There are some things that got put in that should be just taken out. This is one of the reasons the installation ships with the bare minimum of services enabled. On larger and highly available installations the SIP Capture, SIP Trunking and NAT Traversal services wouldn't typically be used.
The sipX system has been around since 2004 and was never really designed to worry about how small a machine it could run on. It was designed to be an 'Enterprise Communications System' (that was the 'ecs' in sipXecs). The 5 to 50 user market wasn't a target market. As such, there's a lot of neat things that piaf can do that sipXcom can't. It doesn't sit in the call path and listen to DTMF tones. Also, sipXcom doesn't support digium/sangoma cards either. It likes off-server gateways and SBCs. The other thing that smaller installations struggle with is the use of DNS. The system relies heavily on DNS SRV records so folks coming from the Asterisk system world tend to struggle with that.
sipXcom is more bound technically by what SIP signaling allows it to do and from a feature perspective what does an enterprise of 500 to 50,000 users need in a communications system. Highly available systems managing 1,000-5,000 users and phones are commonplace on the open source platform. There are 10,000+ seat systems on the commercial platform (HA voicemail / openfire plus a few other commercial enhancements).
Thanks for looking and keep doing great things!