Since you're not using phono, the preamp section is probably attenuating the signal instead of amplifying it, which is why passives work for CD sources.
Without the need to equalize and amplify phono cartridges, the role of separate preamps might be to just increase the number of chess pieces to create the desired complexity to become obsessed with the chessboard in putting together the magic checkmate system. You miss out on that if everything gets integrated. It can save you some money, but a big part of the fascination in audio is the number of pieces and the vast array of choices in combination. Just add the "everything matters" assumption and you're in for years of calculations, research, and nervosa.
Without the need to equalize and amplify phono cartridges, the role of separate preamps might be to just increase the number of chess pieces to create the desired complexity to become obsessed with the chessboard in putting together the magic checkmate system. You miss out on that if everything gets integrated. It can save you some money, but a big part of the fascination in audio is the number of pieces and the vast array of choices in combination. Just add the "everything matters" assumption and you're in for years of calculations, research, and nervosa.