Imagine that you want to create an impulse response from your favorite tube microphone pre-amp, allowing you to use its unique color on your audio. This way, you can run a signal through this impulse response in Space Designer (set to 100% wet) and add the color of your microphone pre-amp to the signal.
This scenario requires neither speakers nor microphones. You can simply connect the output from your audio interface to the input of your hardware device, and play the sine sweep through it. Connect the output of your hardware device to the input of your audio interface, and record it back into Impulse Response Utility. You can use this method to make impulse responses from classic hardware reverbs, multi-effects units, equalizers, and so on.
You should take care when making impulse responses from hardware effects devices that include modulation effects. Modulations such as phasing, choruses, and so on, interfere with the sine sweep itself, which makes deconvolution difficult or impossible. This is also true for some reverbs, such as classic Lexicon hardware reverb devices, in which the reverb tails are modulated. In these cases, you may be better off sending a recorded impulse (such as a recorded spike or gunshot) through the hardware effects device, instead of a sine sweep.