I couldn't get mine to synch going directly from my laptop (PC) to ATV1 using an ethernet cable. Not saying I didn't do something wrong, just saying it didn't work for me.
I have connected my ATV to my wireless router through an ethernet cable and it did synch much faster.
With all that being said, if you're synching an album or two (even in Apple Lossless), it doesn't take that long to synch. I synched 2 double albums a few nights ago in about 20 minutes or so. My wireless router is also about 7 years old, so most likely not as fast as the latest and greatest, and my laptop is 8 years old. I'd imagine newer stuff would be faster.