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I had this same problem after I updated to 4.3. I can confirm that Factory Reset did solve this problem for me.
You need to run a repair process via sony update service to rectify some of the issues.
http://www.sonymobile.com/gb/tools/update-service/
Yes, the REPAIR process via SONY PCC fixed the Sound Enhancement crashing problem for my Z1 running Android 4.3, it also fixed the low volume problem, previously the volume of the ringtone was very low too even at the loudest volume.
I face the same problem when accessing walkman>settings>sound effects> sound enchancements>settings
Repair your phone software via sony update service or pc companion.
After I submitted upgrade firmware to 4.3 (Xpepria Z1) I had a serious problem about my sound enhancement does not work. It doesn't force close. It just has no reaction when I try to use clear audio+ or use equalizer. The sound always just the same. I tried everything such as factory reset or reinstall firmware through PC companion but it still the same. Please send me the way to fix this problem. Listening to music with good quality is the most important thing that I pick sony as my smartphone. Thank you