What do you want the "direct" signal to be?

Just the guitar, after a pre-amp, after a pedalboard, or after the guitar head?

The first 3 can be achieved with a standard direct box.

1/4" cable from guitar > direct box > 1/4" cable through to amp
signal split to also provide > XLR to Firestudio

The last choice, (after the amp) requires a special direct box or other interface with a much heavier transformer in it, that can take the high-output of the amp and step it down to a useable signal. It has to be made specifically for this job so it doesn't burn up the transformer or screw up the amplifier's output stage. You only need a few milliwatts to record, your amp might put out 200 watts or more.

Good luck

those DI boxes that can handle AMP-out usually have a resistive divider to knock the high voltage down to much, much lower voltage and then through the same transformer
...
making it look like a normal microphone source

if it is Line level out ... at say +4dbU ... then the transformer with be a little bigger and of similar size to other line level units

hope that makes sense

No DI box needed for initial recording - the FireStudio Project has two instrument inputs. Just use a TS dual jack adaptor and daisy-chain the guitar lead from the amp into the FS Project. Keep the lead lengths as short as practicable.

Re-amping is a different matter. If you need to do this, get a re-amp box that is designed to take the line out from the FS project and produce a signal suitable for the amp input.

I used to do that all the time with an A/B box and a solid state amp w/o any problems, but when I was using the same set up and an all tube amp I was getting significant hum from the amp. Maybe it was just the use of the A/B switch instead of a Y adapter, don't know but solved it with a DI. The instrument level inputs on the Presonus work great though I noticed just a little more headroom when using the Radial J48.