Yes i know that info on where do place them would be nice.
If you have the CD ROM BIOS, place them in the /3ds/temperpce_3ds/syscards folder.
They must be named:
1. syscard1.pce (version 1),
2. syscard2.pce (version 2),
3. syscard3.pce (version 3),
4. syscard3.pce (arcade card),
5. games_express.pce (for Games Express).
You can have all of them in the /3ds/temperpce_3ds/syscards folder.
In the configuration, you can choose which ROM version you want to use.