This topic was something I was thinking about last night. IMO I think that the companies making reamp boxes and eve DI boxes are completely scamming the electrical illiterate musicians for their money, and the use of a reamp box is precisely only that. I will probably write a Impedance tutorial/lecture to shut up all the conceptions of how all this stuff works, but simply put impedance matching does not mean that you are matching the load to the output impedance that would actually be a mismatch. The input impedance of the next stage should always be at least ten times greater to that of the previous stage output and one hundred times greater in a precision circuit. Impudence matching is only a practice to load the stage high enough to prevent a loading effect.
Simply explained, for a guitar amp, a reamp box should not be needed. The internal output impedance of an audio interface should be pretty small so the high impedance in will load the stage in a way that it operates how it was designed (without a load). The only thing that a reamp box is doing, its not matching impedance, its mirroring the impedance by changing the voltage to current (decreasing voltage, increasing current). However if you are reamping a tube amp, which is a voltage controlled amplifier, a reamp box is doing nothing more than attenuating the input volume to that "SIMILAR" to pickup, but since you don't know the actual output of your pickup, it doesn't really matter. All your doing is dropping over $100 for a fixed attenuation device which you could have easily done in your DAW. Same goes for your DI box, it is increasing voltage, decreasing current and mirroring the impedance, you aren't matching shit.
The reason that reamping without a Reamp box is that reamping still needs a buffer (high impedance in, low impedance out) so that the next stage can be driven correctly. The buffer acts as a current amplifier, giving the voltage the kinetic energy it needs to drive into the next stage. And this is only needed because the output buffer on most interfaces are not strong enough for this function. The opposite goes for DI, since the impedance of the pickup is not at least 10 times less than the input of an interface (though from my experience most interface inputs are high enough to not have a problem (as long as it is around 100K or higher), a buffer stage that acts as an unity gain amplifier with a lowered output impedance prevents the loading effect.
The big concern is the DI though since you have a high impedance into a low (and all that you need is a small signal step up transformer (maybe about $30-50 max)), however in a reamp situation you are going low to high, which is good, you just need that current gain. And a simple $5 transistor project could get you the same place as a more expensive reamp box if you even need it as it depends on your interface.
