Requirements 1 to 4 are fairly easy to check off on many entry level DAC/AMPs. Caveat being most will include RCA outputs for speakers. Fiio K11 (£120) springs to mind, or it's Fiio K11 R2R variant for £150 (this one is difficult to get hold of atm). The K11 is a fantastic budget DAC/AMP with USB-C input, optical input, RCA outputs, external power supply, single-ended and balance headphone output. UAC 1 & 2 modes. Very clean/analytical, neutral and powerful little unit. Bought one soon after they came out and would definitely recommend. The R2R version provides a slightly warmer sound that some might prefer.
BT input is more common on more expensive DAC/AMPs, such as the Topping DX3 Pro+ (£200) or Fiio K7 BT (£230). Possibly cheaper units I'm overlooking just can't think of any.
I can't recall having seen sub output on anything other than separate amplifiers, but this feels like the hardest requirement to meet. I know if looking at external sound cards, like the Creative Soundblaster X4 (£100), this will have PC 3.5mm outputs for speakers (similar to what you find on motherboards). More gaming features and therefore dependant on software and isn't going to produce as high quality sound as the earlier examples.
Hope that helps.
