Alan,
After reading your post, I checked the specs for my Denon AVR-3806:
Power amplifier
Rated output: Front:
120 W + 120 W (8 Ω/ohms, 20 Hz ~ 20 kHz with 0.05 % T.H.D.)
160 W + 160 W (6 Ω/ohms, 1 kHz with 0.7 % T.H.D.)
Center:
120 W (8 Ω/ohms, 20 Hz ~ 20 kHz with 0.05 % T.H.D.)
160W (6 Ω/ohms, 1 kHz with 0.7 % T.H.D.)
Surround (A, B):
120 W + 120 W (8 Ω/ohms, 20 Hz ~ 20 kHz with 0.05 % T.H.D.)
160 W + 160 W (6 Ω/ohms, 1 kHz with 0.7 % T.H.D.)
Surround Back:
120 W + 120 W (8 Ω/ohms, 20 Hz ~ 20 kHz with 0.05 % T.H.D.)
160 W + 160 W (6 Ω/ohms, 1 kHz with 0.7 % T.H.D.)
Dynamic power: 140 W x 2 ch (8 Ω/ohms)
210 W x 2 ch (4 Ω/ohms)
Output terminals: Front, Center, Surr. Back 6 ~ 16 Ω/ohms
Surround: A or B 6 ~ 16 Ω/ohms
A + B 8 ~ 16 Ω/ohms
Do you think I should be concerned since there is no 4 ohm rating, and even at 6 ohm, all channels are only rated at 1 kHz. I have never had a problem with it, but like you say, I'm forcing it to drive three 4 ohm loads and four 6 ohm loads now.