Interesting comments about the HE-500 being bright as I find the treble somewhat recessed and some coloration in probably what is the lower mids or upper bass registers. Never bright. Running it off a DACmini is a dream! Highly recommended and can't wait to try an audeze vegan pad on the cans to see how that goes. Perhaps a silver cable may yield a bit more detail on the top end but not particularly bright. Nevertheless, an enjoyable can that is natural but not what most consider neutral.
If your budget is $600 then a bit more can also supply you with a very good headphone amp/dac package in the DACmini. And if you so wish you can get a more powerful amp at a later stage to suit your needs.