Oh jeez now I have to rethink my whole setup. I always thought that having a separate dac and amp was preferable to a single unit.
Separates and integrated units have their advantages and disadvantages. For combo devices, you avoid longer paths for the analog signal to travel and any chance of coloring it as it doesn't leave that box, in some cases not even the circuit board (believing in cables does not necessarily mean you're the type to blow thousands on them, but actually avoid them as much as possible). For separates it's easier to design a power supply for each device, whereas in devices that integrate both DAC and amp in one box, there is a concern that they might not have a good enough power supply. Most of this is coming from how more affordable AV receivers are designed and rated, and the experiences of people with these devices (and then went around the younger folks here on Head-Fi) : one power supply for the surround processor and 5- or 7-channel amplifier, which is rated as follows for example:
1. 175watts @ 2,000hz, 8ohm load, single channel loaded / 55watts per channel all channels driven ; or
2. 175watts @ 2,000hz, 8ohm load, single channel loaded (nothing follows, then it sounds like crap next to a 2ch integrated amp rated at as low as 25w for Class A or A/B amps)
3. 85watts per channel @ 8ohms (nothing follows, then it sounds like crap next to a 2ch integrated amp rated at as low as 25w for Class A or A/B amps)
Note: I've noticed that more affordable A/V receivers nowadays are sometimes still rated in similar fashion, but have a "discrete amplifier design," which I assume also comes with at least separate capacitor banks for each channel (will confirm once I buy one used and get a peek inside). Regardless I also read less and less complaints on them vs entry-level 2ch amps, now the only argument against mainstream brand A/V receivers is that you won't pay a lot more for Emotiva separates (not to mention you'll probably upgrade the processor every few years anyway)
Another concern is where their money goes: in some devices, it is primarily either a DAC or an amp, with an amp or DAC that sometimes feels like it was just an after thought, or otherwise limited by the PSU design, especially in USB-powered DACs if you're planning on using high-impedance or less efficient headphones on them.
However, it all really depends on the design. Some amplifiers for example use USB DACs that use the 5v from the USB port to drive it instead of sharing the amp's power supply. Or if from the ground up the power supply was designed well enough to power the DAC and amp sections adequately, and each one designed to do its job right, then the gains made in having only one box (no stacking, which might allow for less airflow on the device on the bottom) are more advantageous given the trade-offs are insignificant. Take for example my Meier Cantate.2 amp - it has a basic PCM2702 USB DAC using the same power supply. When using the USB DAC, voltage swing drops only a measly 0.3v from 12v peak to peak to 11.7v peak to peak; at the same time I've pitted this DAC against some entry-level and mid-level CDPs, lo and behold, its small soundstage is at least consistent in imaging in front of my head (the CDPs tend to put percussion all over the place around my head; sometimes other instruments aren't level on the Y-axis either).
