Implementing multiple mappers on a cart would be a difficult (or perhaps impossible) task. Only one mapper was used at a time on a cart as there was no need to be so insane. It is expected/recommended that the bitpack for an OHB specifies which expansion chip to use for an NSF+ compo, unless there is some other strong theme to keep the entries coherent.
Accepted file format
.nsf
Playback (for voting)
Apart from the tools you can use for creation, also:
- NSFplay and VirtuaNSF (version 1.0.6.1 is recommended)
For playback on actual hardware, both the PowerPak and the EverDrive N8 PRO (but not the original EverDrive N8!) have built-in NSF players. Note that if you are using any extra sound chips, they need to be supported by your flash cart, and if you are using a NES (as opposed to a Japanese Famicom), you will need to mod your console to get the expansion audio out of your NES since this functionality was removed on the NES hardware.
Render to MP3
Since NSFplay and VirtuaNSF are both capable of emulating expansion chips, rendering an NSF file with expansion chips is the same process as rendering one without. See here for details.
