Unfortunately SDM will not supported on the 2600, it is supported on the 2600XM boxes as you noted. Neither the Cisco web site and the SDM release notes mention support on the standard 2600s.
But fortunately if your router is 2691 then you can try with new IOS 12.2(11)T6 or later
Please see the below link for Cisco Routers and Cisco IOS Versions Supported.
http://www.cisco.com/en/US/products/sw/secursw/ps5318/prod_installation_guide09186a00803e4727.html#wp37069
Hope this clear you.
Please rate the helpfull posts.
Regards,
Naidu.
