phono stage volume

more likely your preamp has just jacks for external phono preamp.

Buy a new cartridge. It sounds like you are using a cartridge which is too low output for your preamp. Was the cartridge bought new? If so, I would hope your dealer asked you what preamp you are using.

If you do have a preamp for moving magnet cartridges, you will have to get a moving magnet cartridge, or a high output moving coil cartridge. I know the grado high output moving coil cartridges are fine with a moving magnet phono stage.

Phono preamps can require turning up the volume (over other sources). You might try making certain that the interconnects and other cables are tidy and "separated from one another" as much as possible in order to reduce the system's noise level and then see how the phono sounds @ higher volume levels. If it sound good, then don't worry about turning the dial a bit more. It is important to keep the phono cables away from power cords and speaker cable and if they do have to cross one another (can't see why they would though) then have them cross @ a right angle. I am assuming though that the G+ is a MM cartridge with fairly strong output. If it is a low output MC cartridge than, yes, you will need a step up device.

Audioclassics.com sells a Mcintosh stepup device for 300 or so - it is very versatile and will give you what you need to increase gain with variable load capability.

Assuming the Hafler already has a phono stage, just turn up the volume. What you describe is not uncommon.