Just for the record, I would not pay more than USD 1200 for a mint Comet with box and all the et ceteras. Most people bought these when they were offered by Underwood at under USD 2,000 some years ago, so ignore the high list price.
I have no idea why you would want to buy a unit with which you have already had a negative experience. Also, DACs have really improved in both technology and price over the years so you would be buying something rather dated and extremely awkward to use. The single thing to recommend about the Comet is the aluminum case.
I strongly recommend the RME ADI-2 which you can get new for under the used price of this unit. Another fine option is the Topping DX 7 pro plus. Both of these have fine headphone amps built in; the Topping goes for well under USD 1,000. Read some of the reviews on Audio Science Review. Last but not least, both these units and their relatives actually have screens that you can read without a magnifying glass!