Yes sub(s) would be good, BUT ...
If getting subs, get better tops, 12s or 10s
even (smaller tend to sound better in general) and as part of a matched system. It will
sound better, especially on vocals and fiddle.
You have to treat every room as
unique in sound, obviously, but it's even more important with bass frequencies.
With double-basses, it's nice with just a touch
of 40 Hz, so the sub(s) should
have at least some output down there.However
, most double-basses can
sound pretty natural from speakers like yours
But for now, you could try and
borrow even one active sub with it's own low pass filter, and feed it from an aux for that
extra bit of low. and see what you think after some gigs and rehearsals.
--------------------where I live