Came across a simple stereo to mono dsp plugin that seems to work well with ZaraRadio 1.4.4, and I'm not noticing any problem when ACG and crossfade is active in Zara.
It's called "Somewhat Mono" and it mixes the stereo down to so that both channels have identical mono output, which is likely better than using a y-adapter. http://uploadgeneration.info/Winamp/www.winamp.com/plugin/somewhat-mono/142869.html
Anyway, it's free, just drop it in your Zara (v1.4.4) plugins folder and add it, to use it simply move the slider bar all the way to the mono side:
I originally wanted it because I decided to bring the SStran 3000 and a laptop to the pavilion.. They use a single amplified speaker hooked up to Sirusradio and it never sounds quite right, I guessed it was due to only hearing one channel, and decided to hook an am receiver to it instead.. I didn't realize the SStran has a built in stereo to mono mixer, so I ended up not needing this plugin, but thought others might have an interest in it.
By the way if you use Somewhat Mono along with the Sound Solution plugin it really improves the sound while still maintaining the mono, but then you need to turn off Zara AKG or it will stutter (as usual).
You can get the excellent Sound Solutionplugin from Mram's page http://mram.50webs.com/index_files/page4.htm
Unfortunately, Zara 1.4 won't work with Windows Vista and anything later (at least, I've never gotten it to work correctly, it crashes on some sort of callback). You need the latest version (I believe it's called ZaraRadioFree), which doesn't support plug-ins 🙁