Well this gives me an idea for an interesting FPGA project. The early CD players, like Sony D-5 (I just looked at its service manual), have accessible recovered clock and data signals (they are buried in a chip for newer devices). It would not be too hard to make the EFM decoder, de-interleaver, and error corrector in an FPGA so that I can have these features.

How much would audiophiles pay to have a quality indicator on their CD player? Hmm...

Edit: Sony's CXD2500BQ shows error correction information on the pins- no FPGA needed.

CXD2500BQ is used in Onkyo's DX-7310

This company claims to have a product for this (but no pictures..), follow the links for their "CD Errormonitor":

https://www.wpnsystems.com/