The A-603's will provide a 10x step up ratio and 600 ohm load in the 'lo' gain position, or 20x and 150 ohms in 'hi'. Between these two setting, these transformers can match a wide range of low output moving coil phono cartridges to moving magnet signal levels.
The ground switch on this box selects how its aluminum chassis is grounded for shielding, and has 3 settings to allow the box to be wired in a variety of ways. In the center position the box is kept separate from the audio channel grounds and a separate ground wire should be run to your preamp ground post. If you don't want to use a separate ground wire, the "L" position connects the box to the left channel audio shield. This position usually provides adequate shielding and keeps a ground loop from being formed between the two audio shields. "L+R" joins all three grounds, left audio, right audio, and chassis, and will occasionally provide the best shielding, particularly if you use certain cables that might not have both audio grounds tied and both ends of the cable. In general you don't have to worry too much about what the switch is doing, just wire the box how you like, and find a switch position that eliminates hum.
If you have other 9 pin miniature transformers and a reliable pin-out diagram for them, I'm happy to make custom boxes for the same price. Feel free to let me know what you have!