Yeah I've used the lite version quite a bit too on my prevail and they had some cool ones. works pretty nice too.
I've manually changed them quite a bit too. As for your problem with the sound..
the only format that android will accept is "uncompressed audio"
NOT mp3, oog, m4a, etc. only WAV
you can use mp3 but you have to convert it to WAV.
Here is a good free one for windows:
Free Audio Converter: free audio converting software
if you convert mp3 to WAV the volume of it will be low so you have to edit it with an some audio editing program to amplify it and you would also be able to trim it, add effects and such. I use Audacity
in windows and linux cause it's free and it's just as good as a $300 pro app. once you export your edited file, just rename it to poweron.snd (remove the .wav extention off the end) and move it to /system as you do now and it will work just fine.
But the easiest way is to just find the
sound you want in WAV already