Thanks, tisimst, for this thread. As many have pointed out, it is unusually civil and constructive for this forum.
My two cents:
First, I agree with zgas-music about the general principle that "small ensembles" (and, by extension, solo instruments) sound best on one's home system. It's really not possible to reproduce a symphony orchestra in a grand space like the Musikverein convincingly in one's living room. So, from small to large, emphasizing idiosyncratic options others have not yet mentioned:
Solo piano: Beethoven's Sonatas opp. 57 and 111 by Carol Rosenberger on Delos. Not my favorite performances, but strong and confident—and she plays them on a Bösendorfer Imperial Concert Grand piano. This piano doubles the bass strings, and has an enormous sound. Arguably, this is "inauthentic" for Beethoven, as he composed these pieces for the pianoforte, a very different, much more modest instrument. But these two sonatas are "heroic" indeed, and sound "superheroic" on that super piano. The recording was made in 1981, at the very beginning of the digital era (it is a digital recording). Early digital notoriously sounds harsh. Not this CD.
Ivo Pogorelich's performance of Mussorgsky's "Pictures at an Exhibition" on DGG is very natural-sounding. An audiophile friend turned me on to this recording, and I agree with his embrace of it.
Solo violin: Hilary Hahn's first recording of the Bach sonatas and partitas. Unpretentious artistry intimately recorded.
Solo cello: bdp24 recommended Starker on the original Mercury vinyl, and I wholeheartedly agree. I have owned that 3-LP box set since high school, and it is one of my prized possessions. There are three different recordings/performances by Starker; the Mercury set from the early 1960s is the best by far, both for sound and for interpretation. IMO, this is what Bach himself would have chosen from that huge field of alternatives. But I also agree with mceljo that the Bailey on Octave is outstanding, and has great sound. For that matter, Bailey's earlier performance on Telarc is also outstanding in both respects.
ECM has been recommended by several folks, and I will concur there too. Jarrett, of course, but almost anything else as well, including their experimental stuff. Manfred Eicher is a genius, and the guiding force behind the label. If you like choral music, check out Vox Clamantis, a CD called "Filia Sion" (Gregorian chant, with other medieval things done in a slightly contemporary fashion, and gorgeously recorded). But one of my very favorite disks is Arvo Pärt's "Te Deum" on ECM. About half an hour of pure bliss!
For Haydn symphonies (small ensemble performances, spectacularly well recorded), try any of the Orpheus versions on DGG. My favorite is probably No. 53, "L'Imperiale," but they're all good. And available cheap on eBay. The Orpheus performance of Beethoven's complete "Creatures of Prometheus" music is another favorite, and one of my "reference recordings." I've written about it on other threads. If you know Beethoven, you'll know the Overture to this piece, but the incidental music that follows it—an entire CD of little-known middle period Beethoven—is just as compelling.
Haydn's "Creation" ("Die Schöpfung") is another of my reference recordings, performed by Gardiner (his Beethoven cycle on original instruments, which was praised by someone above, is also outstanding), on Archiv. This is a big piece, with orchestra, chorus and soloists, but it is so well recorded here it makes the hair stand up on the back of your neck. And it's wonderful music.
Finally, just to shut myself up: "Uncommon Ritual," an odd but delicious album of miscellany by Edgar Meyer, Bela Fleck and Mike Marshall (so, acoustic bass, mandolin, guitar, and banjo) is really beautiful, and so naturally recorded it feels very much like they're all in the room with you.
FWIW, my wife is a pianist, my daughter a violinist, and I play cello. We play together in the house all the time, so my ears are attuned to how those instruments sound in my listening space. These recordings faithfully reproduce the timbre, scale, and presence of piano, violin and cello with amazing fidelity.