Hi Mark,
If the high end is usually right with most of the CDs you listen to, then the problem with Richter's arrangement of Vivaldi's Four Seasons could well be distortion on the disc. As you probably already know, not all CDs are properly processed and I'm also pissed off with distorted audio sources.
At present, I try to get HD FLAC files of CDs and a lot of them are available now. Of course, if the recording engineer is usually recording pop stuff and doesn't care about the bigger dynamic range of classical music, you won't get a good CD or FLAC file. The FLAC file is usually quite superior though.
Several websites sell those FLAC files, one of them being the British site: PrestoClassical.co.uk. Sooner or later, we will no longer be able to buy CDS. If you prefer to have a reel physical file on a disc as I do, you procced as I do. You transfer the FLAC file onto a DVD-Audio disc using a DVD-R disc. A good software which I use for this is the Cirlinca HD-Audio Solo Ultra 4.4.
Cheers,