Two separate issues; the delay/echo part and the preamp/boost part.
IMO/IME, the echo part is easy enough. It won’t sound like a real EP-3 but nothing does. I agree they are magic but…imo the echo isn’t the thing here. It’s the preamp.
I remember reading how the EP-3 changed the phase a tiny bit (probably frequency dependent) and the Secret Preamp tries to emulate that. I just remember the one I had was very finicky, some amps it enhanced and others it ruined. In the end I got sick of inconsistent results and sold it. But I should admit more and more I’m a straight in guy.
FWIW, I use an El Cap with the preamp off (or at least true bypass, I can’t remember…whatever the least intrusive is) into a cranked Marshall. The echo is close enough and true bypass doesn’t mess with the tone.
Only had one EP-3 but they are a sound to be experienced. Indescribable tho.