Dear Rhy , I recommend using FavorPreptm Stool DNA Isolation Mini Kit or QIAamp DNA Stool Mini Kit that contains optimized buffers leads to removal of PCR inhibitors even DSS. Otherwise a protocol using 4 M lithium chloride in  the presence of 0.6 mg/ml ethidium bromide to precipitate RNA and proteins contained in the DNA preparations may be the choice.

regards

You could try the dextranase(s) to depolymerize the dextran backbone.

Dextran Sodium Sulfate (DSS) strongly inhibited PCR amplification at concentrations over 0.01 g/L. You can use lithium chloride to make precipitation of DNA.