I was looking through ContreBombarde for a suitable Advent voluntary to learn and this piece (specificially David/Agnus_Dei's excellent performance of this piece) jumped out at me, as I really liked it and thought it would suit Armley very well. I hope you enjoy it!
p.s. let me know how effective you thought the crescendi/diminuendos were. I found it a little difficult with just the sequencer pistons. Oh for a full complement of divisionals!