Zephyron,
Upgrading your firmware is always risky, there are so many different versions of firmware now that version numbers like 3.5.35 or 3.5.37 are meaningless as there can be 100's of variations. This makes it near on impossible to know if a particular firmware is going to be compatible with your player or not.
I have personally tested 100's of firmware and I have never gained any new features by upgrading in fact in one case I loaded a firmware that had less features than the original. Others have reported that they have gone from having one game to having 3 or 4 by changing firmware or gained telbook or ebook features that their original did not have and I have heard of one or two who gained file browsing. I would guess that 75% of firmware I have tried will leave my player with a black screen that is easily recovered with reloading the original. 15% will kill the player completely and require a dead player recovery. 5% will not load at all and the remaining 5% will load succesfully. I use 3 different players for testing and in each case I have always returned to the original firmware because there have been no worthwhile benefits.
In answer to your question is it possible to change the music and video interface to make it more compatible with some of the themes, no at least not withourt changing firmware. Some of the skins can be edited to suit your firmware using Photoshop or other image editing software.
Regarding Butt Ugly firmware, most firmware is a little cheesey with flower themes etc and most people are able to change them using s1res and a downloaded theme or by creating their own or adapting another. The process can be quite easy and rewarding but may take a little time to edit or load all the images. Editing your own firmware is quite safe trying to load someone elses themed firmware is risky as mentioned above.
I have however seen 1 or 2 firmware that have terrible themes with love heart menu's, poor quality images and terrible colour schemes. Some can be very hard to customize because of their image layout. For example in most themes the menu's are made up of one or multiple images to make up each menu entry and the images change completely for each menu item. These are easy to theme and you can almost change the appearance completely from a single animated menu icon to an iPod scrolling menu style. Some may need a little creative editing and text string removal but can be worked around. Others have a static background image that does not change from menu to menu only the icon image will change, with themes such as these you can change the images but not the layout so theming is very limited.
Regarding file browsing there are a couple of firmware in the Download\Firmware section that have file browsing but as mentioned it is impossible to say if they would work with your player they did not work on mine. If you are prepared to take the risk and try them be sure you have a backup of your original firmware, but be aware that there are a lot of players out there that have not been able to be recovered, I have one.
A bit long winded but I hope this helps.
