If compression is causing problems stop using compression after all this is why in general we stopped using jpegs, and DDS files come with uncompressed options. Compression is only one of the handful of different advantages you get from using DDS it will still likely be a net gain using uncompressed DDS over PNGs.
I suspect that given the interest in reflections with a chrome effect then quality probably trumps performance in this particular case, its been a while since I read about DDS skymap formats, but i seem to recall there being a number of benefits to using them anyway. I'll see if I cant refind the page... I probably bookmarked it