Coming to Arnold's music was an epiphany to me as well.  The Naxos series
of the symphonies is a must have for you.  I'd also suggest the symphonies
7-9 and oboe concerto on Chandos.  Your discovery is just the beginning
of what will be a fantastic voyage.  I'd also suggest Martinu if you
haven't already been intoxicated by his music.

Stumpf