I've owned two Cambridge CD players, though not the 540C, and a Cambridge 540A integrated amp. I own one of the original Music Hall CD25's now and have upgraded the opamps myself.
The Cambridge stuff is very good for the money but I would definitely go for the Music Hall if you can find one in good shape. The build and sonic quality are up a level from the Cambridge gear.
Upgrading the opamps in the CD25 isn't any more difficult than changing a fuse and the difference in the sound is quite startling. I prefer mine to the much more expensive separate transport and DAC I had before.