.sid (MrSID) files are not in multiband format. They use a proprietary patented format for which there is no open-source version. You can obtain a software development kit from developer.lizardtech.com, after signing up for an account and agreeing to their license. The license does not permit distribution of their software in source form.
Although it is hypothetically possible that someone has developed a .mex wrapper to connect to the software development kit, it would not be allowed for anyone to distribute the complete accessing code. Reading lizardtech's license gave me a headache, and left me with the impression that even a .mex routine that placed calls to their software kit, but did not include that software kit, would have to have its access restricted to those who had signed lizardtech's license. (I have experience in reading license agreements, but that one I would want to run past a lawyer.)
