If your speakers giving good sound below 30 than don't expect your speakers to bang more than it.....!
Kenwood M6930 are good speakers but they do not produce good sound on louder volumes nor they performed good with amp...!
If you are a bass lover than u must install an amp and sub in your car....
A system is always in-complete without a sub woofer and amp...!
Kenwood 3010 is come in 10"....Easily fit with your speakers @ rear....Pioneer 307 and 308 d2/d4 is also come in 10" with other model name.....Do buy it...!