Answering your question:
8 digits = I would use PA,PA. As probably you’re doing already. You could invent mnemonics for it, I wouldn’t do it. But… as it is chess moves and not actual numbers:
These are some considerations I’d take when memorizing chess moves sequences, or games.
Consider 1 move as both white and black. As always white goes first, then colors aren’t needed to be thought of.
Information A: the piece.
Bishop(B),
Knight(N),
Rook(R),
King(K),
Queen(Q),
Pawn (P, only when capturing with a pawn).
Information B: the position
The 64 positions I see them as a grid, all letters are numbers so: A1 = 11. Alphabetically a-h = 1-8. That maps easy to any number peg list. To differentiate twin piece in the same range add the current pos as a single digit
Information C: the move
Two pieces two positions = a move.
Notation: piece-pos, piece-pos
Examples:
e4, e5 = 54, 55
Nf3, d6 = N63, 46
Rfd1, Be6 = R641, B56
Alternative: 3 digit peg list, everything becomes numbers.
How to memorize the moves? Simple.
Select one locus and then divide it in two, and from left to right, up down or whatever choose the first image always to be white and the second will always be black. Person-Object, the piece is the person and the numbers, or the positions are the object. About captures, figure an extra image mnemonic like fire around, dancing. You could omit captures, by simply sleeping in mind that, if something else was in that spot then simply a piece moving into it means capture. Kings aren’t captured so, no problems.
Alternative: only memorize white then memorize black, using journeys. Though for me, makes more sense to memorize the whole move.