Here is a link to the CRS Compatibility Matrix which lists. compatible software for each version of CRS.
http://www.cisco.com/univercd/cc/td/doc/product/voice/sw_ap_to/crscomtx.pdf
The speech server software that can be integrated to work with CRS are:
Scansoft:
SpeechWorks Media Server 3.1.2
Open Speech Recognition Server 3.0.3
RealSpeak 4.0.1
Nuance
MRCP Server 1.0 SP8
Nuance Speech Recognition 8.5
Nuance Vocalizer 4.0.2