If you’re going mono from a reel‑to‑reel, the biggest risk is the classic phase cancellation that pops up when you just stack the left and right channels. The subtle quirks you love often come from those tiny phase differences, so the first thing I do is listen to the stereo pair with headphones that have a wide, neutral sound. That gives me a baseline of what I’m losing. Once I know what the original sounds like, I try a mid‑side mix. By summing the center (mid) and the side difference (side) into separate mono tracks, I can decide how much of the side information to keep. If the side channel contains the subtle shimmer you’re after, you can leave a bit of it in. If it’s mainly causing cancellation, you can dial it back. Another trick is to put a very slight delay—just a few milliseconds—on one channel before summing. That pushes the phase just enough to keep the depth without turning it into a full stereo image. It’s a bit of an art, but you can use a small, transparent delay or a very low‑pass filter on the delayed side to smooth things out. In short, don’t just sum blindly. Do a quick mid‑side check, maybe a tiny phase shift, and keep an ear out for that “extra breath” you want. If it still sounds flat, go back and tweak the side amount. You’re basically sculpting the phase so it stays in the mix, not fighting it.