Here's something you could try - it does not require much effort apart from the install of dBpoweramp and a codec.
Use dBpoweramp's batch converter to convert a bunch of files to another format such as flac (you can specify all files in multiple folders at the same time). Then use dBpoweramp to reconvert to ALAC. Nothing will be lost since both codecs are lossless. Lastly use the AAC optimiser in dBpoweramp to optimise the files for streaming. If you have (say) 10000 files in your library it will take several hours for each pass (less for the final one). For the trial period it is free and fully functional.
Forgive me saying, but I think the logic here is a bit wrong - "I won't re-encode them again just because Roku Player suddenly stopped working with the latest itunes version. " It isn't the Roku player that suddenly stopped playing them. It is Apple who changed something which broke compatibility. This is something that Apple frequently do to many of their "Made for iPod" licensees I am sorry to say. (don't take that personally - just my 2 cents - and me having a pop at Apple)
Roku M1000, M1001, M2000, R1000, Roberts WM-201, Stream 83i