Part of me wants to argue the fact that, "hey, how much money are you making in this music thing?" to justify buying a full PA with a couple of subs? I look at some of the sound equipment I own and most of it was a justification. Heck, sometimes if we're playing a real venue, we don't bring my stuff anyway. Just a few years ago I was ready to take the plunge and invest in my own subs so we'd sound great, and then I thought, "wait a minute..."
It's one thing to continually book your band for $1500 gigs to say "ok, we need a bigger system to handle this workload", but if you're just playing local bars, or aren't always booking gigs, I'd say "you get what we have". I mean, I'd love to use my own big system every time I go out, but there's a $$$-to-gig ratio that must be satisfied. I think in this case (making the bass drum have more 'oomph', just tells me the band's playing too loud. Or the drummer's not playing loud enough. When the band is properly balanced, it will sound full regardless of the amplification involved.
Why not try the easy solution first and get the guitars to come down some? The sexiest thing I ever did was when one of the bands I played in years ago, stayed soft-to-medium most of the night. The audience was literally drawn in (like a seduction) and every now and then we'd go 'BAM' and everyone would shudder. It was quite a experience to see. From what I recall, that band got a few bookings from the people that were watching that night. Sometimes audiences don't need to be beat on the head as much as led where they want to go. Does that sound crazy?
I say save the money and seek out solutions that don't require buying more gear. If you are booking alot of jobs and just don't need the money, then go all the way and get a PA system that's big and over-powered, complete with sound guy. But if you're not at that level, I'd start simple.
Sorry to derail - I'm just reading all these solutions, and it just comes down to spending more money, and I've been there enough to know what "operating in the red" really means.