And he didn't mention
www.goldwave.com, which is what I used when I converted the Das Boot Sound Mod from SH2 to SH3.
Yes, the attributes should be as close as you can get them, but they don't have to be exact. One thing to watch for is stereo and mono. The .wav sound files can be in stereo, but the .ogg files must be in mono, or else. I'm betting that's where your problem is, since I had the same thing happen back when I did that conversion, three years ago.