Schubert, If you want to explore more Malcolm Arnold you are in luck, in spades. You can get complete sets of Arnold’s music, including all his symphonies initially appearing on Conifer Records in a huge set by Sony and a set of just his symphonies by Chandos, on Amazon for less than $30. I have some of each - the original Conifer seems a tad brighter and more forward, the Chandos a bit more ’relaxed’. Either set though is an huge bargain in any event, and the Conifer by Handley might be a bit more in line with the Composer’s intent if that is important to you.
Here is a disc to fool your ’knowledgeable’ friends. A Stravinsky symphony (#1) which sounds more like Glazunov or Rimsky-K etc than the Stravinsky we all know. I have a Decca recording of the Detroit SO conducted by Dorati. This was Stravinsky’s 1st published music and well worth knowing and having in your collection. It can be found in many set’s of his other works.
A couple of English pieces that sound "Irish", pieces by off the beaten path composers that I enjoy. Arthur Sullivan - "The Irish Symphony" by Hickox on Chandos and Granville Bantock - Celtic and Hebridean Symphonies by Handley and the Royal Phil on Hyperion.
Now for some Finnish music not composed by Sibelius, but quite enjoyable non the less. Uuno Klami’s Karelian Rhapsody et al by Petri Sarkari and the Iceland SO on Chandos. If you enjoy this I can recommend his 2 symphonies(#1 &2) on Ondine by Tuomas Ollila and the Tampere PO. I think I prefer #1 more. If you like these his other works are self recommending I think.