Will the AVR-X3900H damage the RP-504C II?

No. The AVR-X3900H is rated for the RP-504C II's 8 Ω load as it comes.

What impedance setting should I use for the RP-504C II on the AVR-X3900H?

None: the RP-504C II is 8 Ω, and the AVR-X3900H needs no change for it.

Is the AVR-X3900H powerful enough for the RP-504C II?

More than you need. From a seat 2 m away, loud 95 dB movie peaks take about 4 W per speaker, and the AVR-X3900H is rated 105 W per channel. Cinema reference level, 105 dB peaks, takes about 32 W.

Does the Klipsch RP-504C II work with the Denon AVR-X3900H?

Verdict

Yes

The RP-504C II is 8 Ω, and the AVR-X3900H is rated for speakers down to 4 Ω, so it drives them as is.

Speaker load

8 Ω speaker, rated down to 4 Ω

Power

105 W

More than you need. About 4 W gives 95 dB peaks at 2 m

How to connect them

Connect the RP-504C II speakers to the AVR-X3900H's front terminals with speaker wire.
Run Audyssey MultEQ XT32 with its microphone at your seat.

Plan the RP-504C II and AVR-X3900H in your own room.

Draw your room in 3D, place both, and see every connection checked and how loud they play at your seat. Designing is free.

Build it in your room

The specs that decide it

Klipsch RP-504C II

Impedance: 8 Ω
Sensitivity: 96 dB (2.83 V, 1 m) in-room
MSRP: $750 each (MSRP, September 2026)

All RP-504C II specs and pairings

Denon AVR-X3900H

Amplifier channels: 9
Height formats: Dolby Atmos, DTS:X
Lowest speaker impedance: 4 Ω
MSRP: $1,849 each (MSRP, September 2026)

All AVR-X3900H specs and pairings

Questions about the RP-504C II and AVR-X3900H

Does the RP-504C II work with the AVR-X3900H?: Yes. The RP-504C II is 8 Ω, and the AVR-X3900H is rated for speakers down to 4 Ω, so it drives them as is.
Will the AVR-X3900H damage the RP-504C II?: No. The AVR-X3900H is rated for the RP-504C II's 8 Ω load as it comes.
What impedance setting should I use for the RP-504C II on the AVR-X3900H?: None: the RP-504C II is 8 Ω, and the AVR-X3900H needs no change for it.
Is the AVR-X3900H powerful enough for the RP-504C II?: More than you need. From a seat 2 m away, loud 95 dB movie peaks take about 4 W per speaker, and the AVR-X3900H is rated 105 W per channel. Cinema reference level, 105 dB peaks, takes about 32 W.

Swap one of them

Klipsch RP-504C II + Denon AVR-X3800HWorks
Klipsch RP-504C II + Onkyo TX-RZ50Works
MartinLogan Motion 35XTi + Denon AVR-X3900HNeeds a setting change
Klipsch R-605FA + Denon AVR-X3900HWorks

References

Specs verified against the manufacturer's published data. Last checked September 15, 2026.

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