Keeping the phono section in the preamp with the line stage is a good move. You avoid the problems of connectors and cable colorations. Connectivity can make or break any system. The phono is likely the highest resolution format currently commonly available; why compromise it??
All you have to do, if worried about power supply noise, is put the power supply in a separate box. If the preamp design is worth its salt (note the caveat), putting the phono section in the box with the line section will offer the least compromise.
All you have to do, if worried about power supply noise, is put the power supply in a separate box. If the preamp design is worth its salt (note the caveat), putting the phono section in the box with the line section will offer the least compromise.