The Regency lets you pre-emphasize the front end of your amp to add sustain and harmonics by adding slight overdrive and extra punch to your signal, without muddying up the notes.
Use the Booster to hit the front end of your smaller amp harder to cause it to break up and deliver natural amp distortion. Combine the Pre-Drive with the Boost for over-the-top sustain.
Connect your delay to the effects loop. When you hit the booster for a solo, the effects loop will automatically activate to engage your effects pedal with a single foot-stomp.