Yeah, if $700 is your budget, then the BF2 is a great option.
I didn't mean to deter you, only sharing my experiences
The biggest difference to my ears is indeed jumping between topologies (DS and R2R). When I compared a $1500 and $300 DS, I could by no means honestly recommend the $1500.
I did indeed notice an improvement with BF2 over my Modi Multibit. It was an "Okay, yeah, this is
niiice."
But, when I first tried the Yggy, it was more of a "Wow!" However, you're paying over double for that slight (relative) improvement.
I could happily live with the BF2 as my end-game DAC. The upgradeability is a huge selling point, IMO, in terms of the total cost of ownership over the years. It does everything I'd want, and without costing a kidney to do so.
I also don't think you'll be returning it.