trace got bought out by gibson but i hear one of the designers or engineers went to start ashdown. so there's a trace of trace engineering there..
i think in most clubs, a 300W head and 4x10 cabs are more than enough if you're just driving thru the amp for the entire venue.. but for small venues, i really think DI is a good versatile option.
Wala Wala provide an ampeg 1x12 combo with its own DI and.. there is a clarity to the bass..
BarNone have a peavy session head.. ack.. couldnt remember the wattage, but it was a 1x15 cab. they used their own DI as well
my experience at smaller outdoor venues is usually a trace head.. about 250W-300W and a 4x10. i prefer 4x10s to 1x15s because of the sheer punch from those tight arse speakers. but i'd love to try a 4x10 with a 1x15 together..
in perth, i gigged comfortably with an Eden Nemesis 250W 2x10 and came out thru the fronthouse via DI most of the time, using my amp more as a bass monitor. these were probably 100-200 people clubs? plus it was a dream to transport everything because.. you are your own roadie (unless you actually have roadies! heh~)
so to answer your question, not every "volume" issue is answered with getting a bigger head or cabs.. i think having a good soundman at the gig who can mix your DI signal is better than getting massive equipment when there's no experience in getting a good mix from the onstage bass amp.