I haven't heard the modified Music Hall's but really like the stock version and have heard good things about the Underwood mods.
The Cambridge is a very accurate and detailed player but also very smooth and "non-digital" sounding for this price category.
The new Moon CD-1 is similar to the Cambridge, but perhaps gives up some detail for a slightly better soundstage and overall spatial presentation.
The Naim in my opinion is in a category of one. The music just tumbles and bounces out of it in a way that makes me happy. It is not as detailed or smooth as the Cambridge or Moon, but it really delivers the essence of every performance it is asked to reproduce. If you like the Naim sound, well, then you like the Naim sound.
Some people (like Stereophile's Jim Austin) have written very highly of the Marantz SA8001, but I haven't heard it yet. I have not been crazy about their other recent budget efforts compared to current players by Music Hall and Cambridge, but apparently the SA8001 is another kettle of fish.
The Rotel and Arcam cd 73 are outclassed by these others, although you might want to listen to the CD192 if it is convenient. Who knows, maybe you will love it.