I always suggest 5751 over AY or AT, for reasons that jibe with what we’re PMing about. People like to just drop any AX tube in a preamp or PI stage, like they are a 12AX7 with less gain, but both of those tubes have differences that make then NOT ideal for drop in replacements in preamp and PI slots that were designed for 12AX7.
Plus, I still see a LOT of misunderstandings about less gain equaling more clean headroom. But, I especially recommend against multiple low gain tubes in a circuit. In my opinion, if it takes more than one low gain tube in the right spot to get the gain range down to what you want, then you’re just using the wrong amp. Two, maybe. But no more. Besides which, I’ll say again, while it may not look “cool” or seem “normal,” you can get great tones out of the Archon with the gain below 9:00. I’ve used 8:00 and 8:30 is extensively, but you can go lower than 8:00. Open up the master some and turn the gain way down. I have some high output pickups and even with a boost on, I can set it to light crunch.