Del spends a crapload of money......on old test equipment

Is the 333hz and 10khz at 25mv all you need? In other words you don't need a wide range?

If so you might make that work. You would need something of accuracy to measure the output level. None of my Flukes for example go to 10khz. I have one that "I think" goes to 6khz I used to use it in the field to equalize rented dry copper pairs to the radio sites. These of course are speech quality pairs so they don't need as wide range response

If you have a decent oscilloscope that would work for level. Google egag for step attenuator. Actually you can make one for audio. What kind of steps do you need?

You can build them with slide switches