In short, Audirvana seems up to the task, while Foobar doesn't
I am able to get pure DSD out of the Foobar. So I feel it is a user setup issue and not software issue. What is the Output "device" that you have selected? It should be the ASIO+DSD one and not just the Topping that you might be selecting. Also under Preference -> Tools -> SACD try to seletc the output Type as "DSD" instead of "DSD+PCM".
That tutorial like that I have provided is excellent resource for setting up Foobar2000. Yes, Foobar2000 setup is a bit technical in nature. Hence most folks here don't want to deal with it. But the gains are awesome, once you set it up. If you think that Audirvana gives you the results, then that should be the way to go for you.
And you are correct - don't mess with DSF files to convert then to 2X or 4X DSD. The PCM files can be converted to 1X, 2X, 4X DSD if you use the "DSD Processor". The only other s/w that does NOT convert DSD to PCM while upsampling 1X DSD files to 2X, 4X DSD is the HQPlayer. But that requires even more complex setup, which might deter folks.
I recently came across a podcast where Peter Comeau from Mission mention that - the reason why people like upsampling to higher bit rates is because it pushes the noise to higher frequencies. Maybe that is why we prefer DSD to PCM? Whatever - but correct mastering is the key to a great recording.