recomended musical sub for 2 channel audio

I am looking for advice on a sub to add depth to my 2 channel audio system. thinking of rel but have never had a chane to listen too.
room is 13 x 26 set along long wall at one end ( not ideal)
system details
proac 1.5 speakers
mit 750 bi wire speaker cable
marsh msd a400s amp
audio research ls 16 pre
cal audio cl 15 cd
mit 330 shogun low impeedance balanced interconect
mit 330shogun rca
I listen to a little everything but love piano, vocals and jazz