Pi + Allo Boss is good enough for 16 bits, compact one box solution with only one external supply. On the other side an external DAC gives more flexibility and extra formats (Dsd, PCM over 192k sample rate).
For the price Allo Boss is a very good solution (excellent bass), for less money you can use an USB dongle DAC (Apple, Meizu etc), but dongle cable could be an issue.