UT2004 Can't Play Stereo Announcer?

I'm trying to mod the UT2004 announcer, and it refuses to play back the files I've added. I know there's nothing wrong with my .UAX repack, because it includes some of the original files, and these announcements are audible.

All the files I used were 22050Hz WAV like the original, however I just noticed that the original files are all mono, whereas the new ones are stereo (2-channel). Is this the sticking point? Is there any way to make it play them without downmixing them to mono?

I'm trying to splice in the UC2 announcer by the way, which is why the files have to be 2 channels. Anyone who knows that announcer will know that it's heavily filtered to give it a broad enveloping soundstage. Downmixing it to one channel kills it.

Seems odd that UC2 would support stereo SFX content, but UT2004 wouldn't.

I wonder if UC2 supported it from the get-go and sound design took advantage, or if someone said "listen to how awesome this announcer sounds if we apply this filter and offset the echo", prompting them to go back and tweak the audio engine.

I'll never forgive them for marooning that game on the Xbox. That particular version of UE2.5 looks quite advanced, and is wasted on all the low res textures etc. I can imagine how beautiful it could have looked. UC2 even seems to have some kind of HDR.