I remembered what may have caused my little imbalance issue: A few weeks ago, I was listening with the 207 for a long time. I had an itch on my face under the earspeaker, so I lifted the left earcup from my head to scratch my itch. Then my finger slipped and the left earcup slammed full force against my head and -you guessed it- formed a seal. I heard the ugliest noise coming from it, like putting a strip of bacon in to a hot oily pan. A loud sizzling sound beyond any stax fart I've heard. It only stopped when I turned off my amp after about a second or two. Ever since then, the stax fart is a lot louder and more pronounced on the left side as opposed to the right side. Also, here's what really bugs me about the imbalance: It only happens in the bass frequencies, mids and highs are fine, and so is imaging, detail and overall volume! I'll try discharging them a few more times and tapping the casing in all manners and hope it works out.
If not, I'll send them in and hope they don't question my reasons... Or I'll upgrade to the L700 that's been on my list forever now.