Organ music will vary by recording, since the organist chooses the registration to match the piece to the instrument.
Two pieces come to mind: Saint-Saens's Organ (3rd) Symphony, which provided the music for Babe and the Toccata from Widor's Fifth Organ Symphony. The first uses the organ as several parts added to the orchestra, the second is a pure organ piece. The Saint Saens symphony is unlikely to be strident in any recording, except possibly for a few very brief moments when flutes and piccolos are pushed. The Widor piece is more dependent on performer, instrument, and hall.
Note that many organs are tuned to an older concert pitch. If Collin has true absolute pitch, he may notice this.
French Romantic organs have some of the best rumble, hum, and purr, especially those by Aristede Cavaille-Coll, whose works are each landmarks in the art. Franck, Widor, and Saint-Saens played on such instruments, or those modelled on them, will -generally- be less strident. There are exceptions.
I'm especially fond of Franck's Cantabile, Piece Heroique, and the Chorale nr 3 in b-Minor. Again, stridency will vary from performance to performance. Franck's work tends to be introspective.
For harmonic complexity, you cannot beat Bach. The problem is that organists like to use the upperwork in the densest harmonies, and much upperwork is strident.
In Bach, look for recordings of the Little Fugue in g-Minor. You might also try recordings of The Art of the Fugue, not necessarily on the organ. A piano or harpsichord performance will avoid the stridency while maintaining all the melodic and harmonic complexity.
Also try the Mahler 8th Symphony. The 2-part recording on Youtube by Dudamel is a wonder, more for the circumstances of its creation. Dudamel got just about every vocalist and chorister over the age of about five in Venezuala in one hall and rehearsed for a week or so. At over 1400 vocalists, it's believed to be the largest one ever. (He uses only 3 of the 4 keyboards the work is written for, either omitting the harmonium or giving its parts to the organ.) The best recording may still be the one by Neuman from around 1980 (plus or minus). The symphony has a few dramatic dynamic moments, but mostly it's a stream of beautiful sound. The opening few bars are louder, in varying degrees depending on the recording.
I once kept a six-year-old tranquil for 40 minutes or so by plopping Walkman headphones on her and playing a tape of the Neuman recording. She sat transfixed the whole time. She'd be around 22 now. I wonder from time to time if she ever remembers that music and wonders what it was.