You can convert the songs within iTunes. First, check your CD import settings to make sure it's setup for higher than 96kps. Then, choose a few songs as a test, right click and then "Convert to..... (be it AIFF, AAC or whatever your settings are)". Then re-try the Match for those to make sure it works.
Unfortunately if you have a lot of music like this, it will be a bit time-consuming to convert all of them before retrying Match. As for which format to use (AIFF / MP3 / AAC) we're not sure if it really matters. I would recommend MP3 or AAC first just because it reduces the upload times if you don't get a match. And then try AIFF for a second pass as you might get a little better results with that as it's lossless.