These are mostly good quality records. Had you considered using a beter cartridge for beter results ? This could make much more of a difference than Preamplifiers and ADC's ? Such as an Audio Technica AT-33EV or even a Denon DL-103 ?
And if it is quality that matters, then a proper Hi Fi RIAA Phonostage ?
Then maybe a much better arm ?
Then, and this is the last one, a Technics SP-10R turntable ?
Hi Fi people use expensive equipment to get very good quality results. The archival community are more likely to use equipment that is quick and flexible. These LP's seem to fall out of the usual requirements ?