i found another 2 receivers that use CX24116 - Kathrein UFS 910 and Humax HDCI-2000 and extracted the CX24116 frimwares from their software:
1. Kathrein UFS 910 software
May 2006 (version 1.02) to Aug 2008 (version 1.06)
CX24116 FW MD5: b728b5d635393a4081e87d30d87a7632
2. Humax HDCI-2000 software
early 2006 (version 1.00.00 - 1.00.03)
Jun 2006 (version 1.00.04)
Jul 2008 (version 1.00.16)
CX24116 FW MD5: 80a75f739ee38406fc9d246998eadd4b
so, taking those facts and
3. Hauppauge WinTV-HVR-4000 software
3.1. Jan 2006 (version 2.113.24030) and earlier - no WinTV-HVR-4000 support, i.e. no CX24116 support
3.2. May 2006 (version 2.115.24146) to Jan 2007 (version 2.119.25023)
CX24116 FW MD5: 417cafd3b10e207e1dba9a03ad63e405
3.3. Feb 2007 (version 2.121.25351) to Apr 2007 (version 2.122.26109)
CX24116 FW MD5: b728b5d635393a4081e87d30d87a7632
4. Reelbox Lite software
4.1. Feb 2007 (version 1.5) and earlier - no HD support, i.e. no CX24116 support
4.2. Jul 2007 (version 1.9) to Aug 2008 (version 1.10)
CX24116 FW MD5: dd8dfdfca6b72462d9db8032f78631c8
5. Dreambox DM800 HD PVR software
May 2008 to Aug 2008
CX24116 FW MD5: dd8dfdfca6b72462d9db8032f78631c8
we can reconstruct approximately the CX24116 firmware history:
early 2006:
CX24116 FW MD5: 80a75f739ee38406fc9d246998eadd4b
Mar-Apr 2006:
CX24116 FW MD5: 417cafd3b10e207e1dba9a03ad63e405
May 2006:
CX24116 FW MD5: b728b5d635393a4081e87d30d87a7632
Jul 2007:
CX24116 FW MD5: dd8dfdfca6b72462d9db8032f78631c8
or
=====
early 2006:
CX24116 firmware version: 1.17.67.0
size: 32548 bytes
md5: 80a75f739ee38406fc9d246998eadd4b
Mar-Apr 2006:
CX24116 firmware version: 1.20.79.0
size: 32522 bytes
md5: 417cafd3b10e207e1dba9a03ad63e405
May 2006:
CX24116 firmware version: 1.22.82.0
size: 32501 bytes
md5: b728b5d635393a4081e87d30d87a7632
Jul 2007:
CX24116 firmware version: 1.23.86.1
size: 32674 bytes
md5: dd8dfdfca6b72462d9db8032f78631c8
======
so, the latest available version of CX24116 firmware is 1.23.86.1. probably, because it's the latest version, it contains some small bug fixes and that is why maybe it is the recommended version.