Hello,
Although there were no significant performance improvements in JPEG2000 codec since IPP 6.1 but there were some bug fixes in UIC, so I would recommend you to consider migration to the latest version, IPP 7.0or 7.0.2 update which is coming soon.
Performance heavely depend on number of factors, for example encoding options (lossy or lossless, progression order, code block size and so on).
Note, threading on UIC codec level is already integrated in UIC DLLs (if you use precompiled UIC DLLs) or should be enabled automatically when you rebuild UIC codecs with using build scripts coming with sample (and compile by Intel compiler). You may check how many threads used by UIC codec with NOfThreads() method of JPEG2000Decoder class.
Since you have access to completely independed image tiles in JPEG2000 compressed format I think it might be more efficient to not use internal threading at codec level and rather to decode several tiles in parallel (you will need several copies of JPEG2000 decoder, one for every thread you launch). The reason is that in this case amount of work done in parallel is much bigger than in case you use internal threading.
Of course, internal threading might help you to maximize performance on many cores systems (like 12 or 16 threads), where it is possible to decode 6 or 8 tiles simulteneously and to enable each decoder to use 2 threads internally, that will useprocessor capabilitieson all 100%.
Regards,
Vladimir