Mon May 04, 2020 10:17 am
To add to other’s replies.
The dragonfly and the MODI are billed as "driverless," but that's not totally true. They use the computer's "class compliant" drivers, so a driver doesn't need to be installed, but the device can still run into problems when you use them with other software or hardware. Also, as Martin mentioned, the class compliant driver may have a higher latency if they are designed primarily for listening to audio.
DAC stands for digital audio converter, which is the process a computer uses to convert digitally stored music information into an analog current for playback on speakers, headphones, etc. The reason why it improves audio quality to have a good quality DAC is that the better clocks used in a good DAC convert the signal in a way that you get less "timing errors," which are interpreted by the ear as noise. Timing errors can be created both during recording (depending on the ADC, or analog to digital converter used), and during playback (which uses the DAC). Some DAC's are better than others, but most people won't hear the marginal difference between many of the higher end DACs. The dragonfly and the MODI are considered pretty good DAC's, but I would say that the difference between those and the good quality DAC on a digital audio interface would be very difficult to hear the difference, especially using Hauptwerk, whose samples generally have all been very well recorded and have a very low level of timing errors to begin with. As Martin pointed out, however, they may have significantly higher latency than an audio interface designed primarily for production. As for DAC’s, there is a big subjective component to whether or not an improved DAC is worth it (i.e. the decrease in timing errors isn’t audible to everybody, and it depends on the quality of music you are playing), so that is why if you go with a pure DAC, I would recommend you using the solution you choose with your system if possible to see if the decrease is worth it to you.
The extra features on a digital audio interface seem to be a waste in money, but I have found them to be useful over time. Because I am more tech and audio savvy than most people, I have been called upon to record audio on more than one occasion for various reasons. Also, it’s good to have headphone backup in case you would like to practice at night, have trouble with one of your monitors, etc.
It is a forum consensus that the more output channels you have the better. This is because if you ever want to improve your audio from stereo, the way to do it would be to add a subwoofer, extra channels, etc. A subwoofer adds a significant amount of realism to pedal stops, and extra channels add more realism and spatial depth to the main organ output. For this reason, it is usually recommended when a forum poster asks for audio interface recommendations, that they buy as many output channels as they can afford, for future expansion possibilities. As François suggested, since the increase of price from 2 to 4 channels is pretty small, if you are in the market for a 2 channel, it would make sense to also consider a 4 channel. I bought a 2 channel Steinberg UR22 many years ago, which works well with Hauptwerk, but when it comes time to replace it, I will probably buy one with many more channels.
Whatever you end up buying, the main thing is that you are happy with the result! There are a lot of ways to go with a Hauptwerk system, which is why experimenting to see what sounds the best to you is the way to go. You could still go with a Firefly or similar DAC, with the caveats listed above, but you may need a third party ASIO driver to make it work well with Hauptwerk, provided the latency with this combination is acceptable to you.