That makes me particularly pissed that after ~30 days of hemming and hawing I bought SL-rated ATX's 3 months ago LOL.
You're past their 45 satisfaction period, but find out when the C's came out... and if it was before you bought your SL's and they STILL don't have the C's on their website, contact them and make the case that they should let you swap (and pay the difference, as the C's are likely more expensive). You never know, they might say yes...