Specs don't tell the whole truth. Just because a speaker claims to be able to produce a 38Hz sound doesn't mean it is FLAT down to there. You get what you pay for. A Mackie HR824 is ±1.5 dB, 37 Hz to 20 kHz. And a pair of those will set you back $1400 or so. Pair of 6" Rokit's is maybe $400.

You are going to need a powered sub with those or you'll blow them up trying to get the lows that a pair of 15"'s will deliver.