Itdeptcorp,
I would recommend you use a custom theme instead of trying to get a 5.9 theme working on 6.0. I shared some comments in the post Martyn pointed to about the reasons why.
Regarding custom themes etc. for Aware IM applications. I have done several custom themes and UI work and entails all from basic theme changes like changing theme colors, changing parts of themes, to more advanced things like full blown custom themes using integrations with other UI frameworks, to UI/UX stuff like integrating Googles new "Material Design" principles.
I do provide UI consulting for Aware IM developers and can basically do whatever you want in terms of UI. I also provide UX consulting focusing primarily on Material Design (i.e. rework application UI and UX to fully (95%) follow Material Design principles). I can also help you with custom html/css/js modules like for example a custom tree menu if interested.
If you want to hear more or want to ask me questions about this please send me an email at: info@awareim-consulting.com . If you have specific requirements or a project in mind, please tell me a little bit about it and I can share my thoughts on options and also send you some samples, screenshots of custom stuff I´ve already done.