4ohm vs 8 ohm

[kubeek]

Hi, im am designing an amp for bass combo, and I would like to achive 750W. This lead me to choosing between 750W into 8 ohm and limiting for 4, or having 750W into 4 ohm and less into 8 ohm.

From this I realized that since I am building a SMPS for it as well, I could create double rails and let the user switch which speaker he is using.
What do you think about this?

 

[luka]

if you go with class D amp in the first place, you need supply that will make what you want into 4ohm.
I guess if amp is AB, I would still do the same

 

[kubeek]

Exactly, that is why I will use 2x42 with high current and additional 10V per reail for a little lower current.