One way to check if unsure is to try various software settings and other configurations and take square wave or impulse measurements. That usually offers up clues. But it probably does OS. That was one thing I was worried about when looking at 1541-based DACs. Too many people saying they were polite, mid-centric, and so on. I think this primarily comes down to implementation. The 1541 DAC I ended up getting, aside from the usual, very slight treble roll-off from being non-oversampling, has great extension, great dynamics, and plenty of slam even when I compared it against the Theta Gen Va. But I don't doubt most implementations don't have this.