Some monitoring controllers are not just equipped with analag but also with digital inputs. On more expensive controllers the conversion is audibly better than with a middle of the line soundcard. Some manufacturers also offer combination USB-audio interface / monitoring control solutions.
Some, but by no means all monitoring controllers are equipped with high-resolution meters. This is handy, because a hardware display offers a better view than the digital meters of the software. If the controller is connected via a digital input, the display can even work with absolute precision, so that there is an indication when a maximum level is exceeded by even the smallest amount.
Most monitoring controllers do not require a remote control because they are in a practical console housing which can be set up in the immediate vicinity of the central listening position. Other controllers are designed as 19 "rack units to keep the work area free from cables. To use a monitoring controller in a rack housing from the best listening position, you need a remote control, which you should plan to purchase along side the controller.
Some monitoring controllers are equipped with functions that allow you to create a mix for each individual musician being recorded. On one hand, they may want to hear their own signal, on the other, they may want to hear already recorded tracks to orient themselves. Some controllers do this with a small integrated mixer, others with a fader. For controllers that do not have these functions, you can use a smaller external mixer or the sound mixing software on the soundcard.
Its relatively straightforward to manufacture a passive controller with just a volume pot, but features such as mono switches and headphone amps need active circuitry. As with anything, to a certain degree you get what you pay for, and good quality active circuitry tends to come at a cost, so its sometimes better to opt for a passive rather than active controller if youre on a restricted budget, as you will generally get better audio quality for a given price. As an alternative, some designs maintain a passive path for the main signal, but use active circuitry for a headphone amp. If you want anything but the most basic features though, youll have to go for an active design, but remember that every switch and potentiometer colours the signal to some extent, so unless you can afford the very best quality, you might want to choose something that has just what you consider to be essential, rather than go for the model with the longest spec list.
The control surface is an invaluable piece of equipment found in numerous project and large-scale studios, offering control of various parameters of your DAW software. So why not just use one to act as your monitor controller? One reason is that as the control surface is only controlling your software and not the audio directly, it will not be possible to use it to rectify any horrible digital noises caused by crashes or freezes of your DAW - no amount of knob twiddling will protect your speakers from digital meltdown! Of course there are also more obvious benefits to the monitor controller which are not available on the control surface such as accommodating multiple audio inputs from CD players and master recorders, and also many of the other features mentioned earlier in this guide. Having said all this, some high-end hybrid controllers are now starting to appear with analogue monitoring sections built in.
A regular small mixer will be adequate for some set-ups, and features such as mic pre-amps and EQ can be useful additions, but using a mixer in this manner adds unnecessary length to the monitoring chain, and can colour the signal as it is routed through EQ and gain controls - leaving an EQ section flat does not mean that the signal is unaffected. If youve used the same mixer for a number of years, its possible to be aware of the effect that your mixer has on the sound and to compensate for it. This is not ideal, but can work if youre on a tight budget, although of course most small mixers will not offer the kind of feature set found on even an averagely specified monitor controller.