Buy some new CDs. (Try a few XRCDs in particular.) Definitely more value added than any $100 hardware upgrade.
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I agree with Bomarc. Besides CD players and DVD players will sound very very similar with your current amp and speakers.
An external DAC using a DVD as a transport is a crapshoot as the quality of the digital signal from the transport may undo all of the good qualities of the DAC.
And to really upgrade the CD source you'd need to spend nearer $300, rather than $100.