My impression on rail voltage for a phono preamp is that it does not need to be all that large. An output swing of say, 2Vrms would likely overload the following line stage. 48Vdc rails are simply not needed to supply that, although they certainly would work in that application. Again, it's like asking for a drop forge when all you need is a tack hammer.Have you not understood the issue here or you are just going with the manufacturers "vibes"? How do you expect a battery operated amplifier be better than the one that is operated at 48VDC?