F-6 (Linear phase, Fast roll-off) is the most technically accurate, but you're not going to hear any difference or supposed to anyway if the DAC is well designed.
From here, excellent read:
Does your DAC let you choose the output filter? What do they do. How do the different kinds differ from each one? Which is the best? Which is the worst? We'll help you sort it out.
addictedtoaudio.com.au
Regarding the manual, with all due respect;
Topping is a far east company, after the next product rolls out the "old" ones (few months) are history, forget about fixing manuals, PDFs or even bugs.
If it doesn't directly impact sales, forget about it.