Orpheus, if you’re in the digital domain, most likely the 6922s in your source equipment are only serving as a buffer stage, to reduce output impedance or in hopes of the designer to generate a more tube-like sound (I mean this in a good way). Buffer stage does not add any gain and therefore has very little sonic signature.
To whoever asked: 6FQ7 is electrically identical to 12AU7. With one important exception. Before you make such a swap, you need to know what filament voltage is provided by your circuit. 12AU7 can be configured to operate off either six or 12 V filament voltage. 6FQ7 requires 6 V, only. If your particular circuit provides 12 V to the filaments, then you need to use a 12FQ7. Such tubes exist, and they are usually cheaper than 6FQ7, because demand is lower. Once you get the filament voltage right, you can drop in either of those tubes in place of a 12AU7. The other tubes You listed cannot be used without rewiring your tube sockets. I have replaced 12AU7s with 6FQ7s several times, and the result is always an improvement. 6CG7 is another great option but a little easy re-wiring is required IIRC.
To whoever asked: 6FQ7 is electrically identical to 12AU7. With one important exception. Before you make such a swap, you need to know what filament voltage is provided by your circuit. 12AU7 can be configured to operate off either six or 12 V filament voltage. 6FQ7 requires 6 V, only. If your particular circuit provides 12 V to the filaments, then you need to use a 12FQ7. Such tubes exist, and they are usually cheaper than 6FQ7, because demand is lower. Once you get the filament voltage right, you can drop in either of those tubes in place of a 12AU7. The other tubes You listed cannot be used without rewiring your tube sockets. I have replaced 12AU7s with 6FQ7s several times, and the result is always an improvement. 6CG7 is another great option but a little easy re-wiring is required IIRC.