Classical composers, symphonies

If we are including Hindemith, we should mention his most popular work: Mathis der Maler.

And since you like Mahler, you should definitely check out Shostakovich and Britten.

Kodaly, Rachmaninoff, Sibelius, Ravel, Prokofiev, Chausson, Ibert

Or how about Elgar's Enigma Variations and In the South

Rimsky-Korsakov's Scheherezade and Russian Easter Festival Overture are both pieces you'd likely enjoy.  They're program pieces and not symphonies, but still large orchestral works, and the Russians write for brass better than most anyone else.  

One thing is to have the impressing work for big orchestra from Bruckner, Vaughan Williams, Mahler, Shostakovich, Stravinsky u.o. but then if you are an audiophile, it is most important that the performance is well recorded. Honestly, most recordings out there are very average sounding, but it needs good equipment to hear the difference. After extensive search I found the best records ever made of Bruckner, Mahler symphonies and Holst's The Planets. Check it out on my website www.ecliptic.ch/audiophile