While iTunes Match initially ignores your legacy DRM iTunes purchased content, leaving it at 128kbps, you can convert it to iTunes Plus and free your music from DRM by deleting the track and re-downloading.
From "Protected AAC Audio File"
... to "Purchased AAC Audio File"
Nonetheless, Apple has maintained the iTunes Plus upgrade menu for the more distracted iTunes customers.
For many of us who have been buying from iTunes since the beginning, our iTunes Plus upgrade ran many times more than the purchase price of iTunes Match. Mine was about $280. iTunes Match has already paid for itself for about the next 10 years
From "Protected AAC Audio File"

... to "Purchased AAC Audio File"

Nonetheless, Apple has maintained the iTunes Plus upgrade menu for the more distracted iTunes customers.
For many of us who have been buying from iTunes since the beginning, our iTunes Plus upgrade ran many times more than the purchase price of iTunes Match. Mine was about $280. iTunes Match has already paid for itself for about the next 10 years