Based on formfactor, probably the Hiby M300? The 507 is unique in that it's pocketable. There's always the replacement dap from Sony, which is the NW-ZX707, but it's quite a bit larger.

Generally in my experience the only time the database checks/updates is when removing or installing a new card. Once the database has been checked, the walkman should just boot normally in my experience, unless there's an issue with the card. I'd possibly try another card or maybe re-format that...