I think the better question is why do you think that your next upgrade step should be a new DAC? What do you think you’re missing with your current all-in-one A6? I’m not one to tell people how they should spend their money, but the biggest bang for your buck would likely come from replacing your vintage speakers. I think your speakers are your limiting component. The correct path depends on your goals. I suspect that it’s unlikely that you’ll realize improvement that you can hear with the budget that you shared; however, you may find a better return investing that money in better speakers. Again, it just depends on your goals.
And to answer the question that you may ask, " what's wrong with my speakers? " There is nothing wrong with your speakers if you're happy with them but understand that they may not be revealing enough to convey Sonic improvement from a sub-$3,000 DAC. I imagine that if you're going to spend good money, then you want to hear an improvement. I propose that you audition both a DAC in your price range and listen to different speakers that you would consider as your next step up. That way you can make an informed decision without buyer's remorse.
