IIRC, "event-style" wasapi is only supposed to enable the DAC to pull the data stream from the computer instead of the other way around making sure that the dac is the one that is doing all the synchronizing and not the usb host computer therefore eliminating the aforementioned issue.
Yes, Event Style reduces operational overhead and allows almost direct to driver access.
In some cases, the popping problem with WASAPI can be USB-compatibility/latency related. Connecting the device to a port with a separate root hub or to another controller altogether often solves the issue.
If your USB controller happens to be from ASmedia, VIA, or some other less popular brand, do not rule out the compatibility issue possibility. Intel, AMD and NEC USB Chipsets have the best compatibility afaik, because of their popularity.
For me, on the Musiland USD 01 foobar running ASIO sounds better than WASAPI.
ASIO allows true integer transfers (though this is no assurance that the driver handles the data in native integer form), while WASAPI uses FP which is reconverted back to Integer. The latter allows for very minute quantification errors, depending on implementation (not true bitperfect, but essentially bitperfect).
Musiland's different driver paths do sound a little different though, which may be the biggest reason for the difference that you noticed. One path often sounds better than the other, depending on how it melds with the rest of the system. Driver updates for Musiland products also often include firmware flashes, which can make changes to the sonic signature.
Also try setting the sample rate mode to Precision. This can reduce jitter and spdif lock issues.