I would get the period instrument Beethoven 9-symphony box set by conductor Jos Von Immerseel --- it is the greatest music ever written, is very well recorded and sounds simply stunningly good, and is exquisite in every way. Also, the 5 Beethoven piano concertos, again on period instruments by Hogwood and the Academy of Ancient Music is as well stunningly well recorded and is of great music performed impeccably. Bruckner's 8th Symphony by conductor Gunter Wand is as well extraordinary in performance and sound. Finally, a label to look at that uniformly has outstanding sound is BIS. Find a piece you like and see if the BIS label has a recording --- that is, if sonics are the primary concern.
Enjoy.
Enjoy.