I'm really confused what causes the problem.

I had Axiom speaker M80 and QS8, Denon 1908 receiver along with my OPPO 980 DVD player for 4 years w/o any problem. 2 months ago, I purchased SONY BDP S-590 BD player. The player works fine. About two weeks ago, when I play the planet earth BD, suddenly I realize the front right speaker has no sound. Then I tested other DVDs with both my SONY BD player and my OPPO DVD player, I get the same problem. But if I play a CD w/o using HDMI connection, the sound are fine. I changed the speaker connection wire (Raptor 12 gage wire), different HDMI cables, and different pair of speakers, the results are the same. when play DVD/BD, sometimes, the Denon receiver enters into protection mode (I remember this happened once before the sound problem appeared)
I thought the receiver may be damage. So yesterday I borrowed an unused Pioneer 521 receiver from my friend. This morning, I played CDs with my Oppo DVD player, I think the sound is fine (But I could be wrong since the default one is surrounding mode. Too bad, I can't recall if I actually checked each speaker). Then play the same planet earth BD and I realized there is no sound from front right channel too. Further diagnose showed this is true for both my BD and DVD player, w/ or w/o using HDMI connection for the Pioneer receiver. (The Denon w/o HDMI connection is still fine).
I'm confused about what's wrong here. The SONY BD player damaged both receivers? or something else. Any help is appreciated.