As Fafafion suggests, you could start to think about component upgrades. If you find the right combination of pieces, the poorly-recorded music can sound much better.
There is a caveat, though. Systems, and people's listening tastes, can take different directions. Some like a setup that can pull the last squeak of detail out of the recording, revealing the mechanics and structure of the music like sunlight on Mercury (the planet, not the label). Systems like this can make the poor recordings stand out with embarrassing clarity.
It is also possible to build a system which, while still providing piles of detail, doesn't make you want to sideline a great performance just because the recording is blah. If this is the kind of system you want, build it by shopping with your favourite poor recordings among the test material.
There is a caveat, though. Systems, and people's listening tastes, can take different directions. Some like a setup that can pull the last squeak of detail out of the recording, revealing the mechanics and structure of the music like sunlight on Mercury (the planet, not the label). Systems like this can make the poor recordings stand out with embarrassing clarity.
It is also possible to build a system which, while still providing piles of detail, doesn't make you want to sideline a great performance just because the recording is blah. If this is the kind of system you want, build it by shopping with your favourite poor recordings among the test material.