Siblings in Klipsch's Reference Premiere (RP) II series, so they share a family sound. It comes down to size, output and price.
| Area | Better | Why |
|---|
| Bass | A | Klipsch Reference Premiere RP 500SA II digs deeper - 58Hz against 87Hz. |
| Amplifier needs | evenly matched | Similar sensitivity (93dB vs 94dB) - both want much the same power. |
| Size | depends | Klipsch Reference Premiere RP 500SA II is easier to place; Klipsch RP-404C II is bigger, which usually goes with fuller bass. Your room decides. |
| Type | depends | A Passive Surround against a Passive Center Channel - a different job rather than a better one. |
| Cabinet | depends | Ported vs Sealed. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Price | A | Klipsch Reference Premiere RP 500SA II is cheaper - $450 against $599, about 25% less. |
A Klipsch Reference Premiere RP 500SA II B Klipsch RP-404C II
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Klipsch Reference Premiere RP 500SA II has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 87Hz anyway, so judge these on the other rows instead.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.