Isn't it a passive box so the max output is determined by the input signal strength coming from your interface?
Yeah, it’s just that it attenuates way too much for any typical interface D/A levels, assuming you track humbuckers. Some radial boxes attenuate a lot too, as did a D.A.V Reamp I tried.
If you record very weak single coils, record close to 0dBFS, and have beefy D/A it’ll probably do unity.
But it’s basically impossible for it to put out enough signal if you record humbuckers.
There are many passive boxes that’ll do unity, it really just depends on the ratio of the transformer used. Some even have room for a small boost, like the Signal Arts/United reamp box.
Most interfaces output 16-22dBu. Some’ll output 24dBu, very few do more. Typically consumer grade stuff will be less than those values. I’d say that a reamp box can attenuate, but it should still be able to output 12-13dBu when feeding it a 22dBu signal. If it’s attenuating more than 10dB, you’re going to have a hard time hitting the amp hard enough to reach unity for all guitars and pickups. I’m pretty sure the IK reamps attenuate a LOT more than that. I remember trying the DAV reamp box (
http://www.davelectronics.com/di and reamp.htm ) and it attenuates 30dB. Totally useless.
IMO the ideal is to have a 1:1 transformer, and then an attenuation knob. That means the user can get away with using some consumer grade stuff, but it’ll also play nice with pro gear.