Sibelius for me is Osmo Vanska on BIS. In general I am not a fan of the Naxos sound. Have only a few of their recordings that I like: Elgar Second Symphony and Delibes Sylvia Ballet. But I'll check Leaper's.
Well Recorded Classical Symphonic Recordings
I enjoy all genres of music but especially large scale Symphonic works. My audiophile journey has been an effort to reproduce that music convincingly. I remember my first Symphonic concert that I attended. It was the Philadelphia Orchestra conducted by Stokowski as a guest conductor back in the 1960s. At the time I had just purchased a small tube based separates system fromEJ Korvette in NJ. It was $99.00 and had two small book shelf speakers, a Garrard Turntable and a very small10 watt tube amplifier. Sounded great to me at the time. When I attended this concert I was struck by how silken the strings sounded and how warm and burnished the brass sounded. My small system was not anywhere close to this sound.Thus began my journey to get closer to the real thing.
Now that I have finally gotten significantly closer, at the age of 77, I am enjoying my recordings more than ever. I am always searching for well recorded Symphonic music. In my experience it is very difficult to properly record a large orchestra. There are too many variables: microphone placement, types of microphones used, the actual venue which has a significant effect and the tastes of the producer, etc. I find the variability frustrating. There are recordings from the early 60s before multi-track and multi microphones recordings that sound better than those recorded recently.
Anyway I have been able to discover many excellent symphonic recordings that I will share with you. You may disagree but I enjoy these very much and as my system has evolved with better equipment these recordings have revealed more and sound even better.
Tchaikovsky Symphonies - Pletnev and the Russian National Orchestra on DG.This cycle offers the best recording I've come across and it gets better as your system does. Plus the performance is spectacular. Try the Capriccio Italian which is included for a sonic spectacular. Actually all of Pletnev's Russian National Orchestra recordings on DG are excellent.
Beethoven Symphonies - These works have been a challenge for me. It's has been very difficult to find an acceptable recording. With Qobuz I've recently surveyed many recordings. Most are either too closely recorded, have the balance off, or a weird interpretation. As an aside I rarely like live recordings as they are miked too close to reduce audience noise and restrict the stereo spread and depth.The exception has been recent live recordings by the Boston Symphony which have moved the perspective back and allowed the Orchestra to breathe. Plus they have an excellent venue. Back to Beethoven. Not surprisingly I found the best recording again to be Pletnev's cycle with the Russian National Orchestra. Perfect balance, perspective and soundstage depth plus another great performance. I think the venue they use for this Orchestra is excellent and it reminds me of those great analog recordings Decca did in Kingsway Hall.
Rachmaninoff Symphonies - Pletnev again for all the same reasons.
Tchaikovsky Ballets (Swan Lake, Sleeping Beauty and Nutcracker). Pavo Jarvi on the BIS label. Very well recorded and a blazingly exciting performance.
Prokofiev - For the Symphonies the cycle on Challenge Classics in HiRes with the Netherlands Radio Philharmonic conducted by James Gaffigan ( not the Comedian). Prokofiev deserves a wide dynamic and spacious recording with a deep low end. These recording have it. For the Prokofiev Ballets: Romeo and Juliet with Ashkenazy on Decca and for Cinderella it's Pletnev again on DG. Both excellent recordings.
Finally for Mahler - I'm torn between the Boulez cycle on DG which is very well recorded and the various recordings on Telarc. Mahler needs a really dynamic and spacious approach to recoding his works. Both of these deliver but have different perspectives and sound quality. Both excellent but just different. I think I tend toward Boulez based on performance. His approach is the polar opposite of the classic Bernstein recordings which to me are overly dramatic.
Anyway my search continues.