Buy a sub or ditch my new speakers altogether?

I recently picked up a pair of B&W 602.5s, brand new, for a song. Turns out to be the wrong song, and it was a final sale. :/

They have loads more midrange and high end detail than my former Allison CD6s, but the Allison's 8" woofers had the B&Ws beat in the low end.

The B&W's lows are boomy and pretty out of control, and when listening to TV at a lower level, there's almost no bass at all. The port plug tightens up the boominess, at the expense of even less bass overall.

So, the question becomes, do I put these brand new B&Ws up for sale, and look for something else, or do I pick up a subwoofer and attempt to salvage the sound? I am quite happy with the 602.5's mids and highs. I find it interesting that many reviews of the next (discontinued) model up, the 603, mention needing a sub, despite having a dedicated 6.5" bass driver.

If I do end up getting a sub, for say $500, I'm then into the current setup for $900. This begs the question, what could be had sans sub, with similar punchy mids and clear highs, but with deep(er) clean(er) bass, in the same price range?

Logic tells me that a 2 mains and a sub beats the low end capabilities of a $1000 speaker with no sub.

Many thanks for any advice.