I put a pair of gnx 104's in a 3.7 cu. ft. box tuned to about 35 hz that i made using a computer program. Is this box any good for these subwoofers, on the program the spl peaked at about 98 at 50 hz and the -3 db cutoff was at about 30 hz, is that ok for a subwoofer, it sounds pretty loud, i am not very concerned about transient response, i am mostly conserned with spl because i want to get the most for my power also i have about 200 watts total going to both wired in a series to 8 ohms and when i turn it up pretty loud it looks like the subwoofers are reaching their 6.1 mm xmax, i was wondering if since i hear no distortion at all how much more power can i give them when they look like they are being stressed. Also i was wondering why they appear to reach their limits at 200 watts and together they are rated for 350 watts? And why do polk gnx series subwoofers have such a low xmax? Most other subs have at least a half inch xmax.