You'll want to use a high current power supply with current and voltage meters so you can make sure it won't harm your equipment if an amplifier takes up to much current. If you need more amperage, you can connect two high current power supplies together in parallel.
Conversion of any kind is coupled with losses. Why do it? Just buy the appropriate amp for the application and have at it. I see alot of threads where guys are running amps off car batts indoors to power their subs. Not only is that not efficient but dangerous.
