I was given, then repaired a broken Live Wire Solutions SPDI Direct Box. This is a passive DI box, but after acquiring the schematic I determined it can be used for direct profiling within power limits and attenuation settings. The attached spreadsheet and schematic list the resistor voltages and the power ratings are based on the attenuator setting at 0, -20 and -40db for 4 and 8 ohm loads at output wattages at 25, 50, 100, 200 and up.
I checked the math against scope measurements into a dummy load. They are correct
For a 0 - 25 W amp MAXIMUM, a 0 dB setting is acceptable.
For a 0 - < 400W amp -20 dB setting is acceptable, 0 dB is unacceptable (@ 400w into an 8 ohm load the wattage is exceeded on R2 10k ohm unless it is increased to a 1W resistor..)
@ a -40dB setting the attenuation is sufficient to use the DI box but the signal may be too attenuated at lower wattages.