Yamaha voice SysEx dumps (.syx) can be converted to Propellerheads Reason presets (.repatch) using the online PX7 Patch Conversion Utility available on Propellerheads website. This is most likely your best and also only option how to achieve syx to repatch conversion.
Open SYX file Open REPATCH fileA utility for converting Yamaha DX7 SYX format