The math is simple: You need to match the input sencitivity of your preamp and approximately calculated output from your phono. The voltage gain of 57dB has a factor of >700 so .3mV in the input will give you >210mV in the output which should be good enough for any preamp except passive. .8mV version will be good enough to couple with passive preamp. Staying with lower version gives you an advantage of small signal path and great detail and transparency. Higher outs are just suitable with more phonos but compromise in everything else.
