They usually have only one input and no remote. What are you going to do if you want to listen to more than one source, keep plugging and unplugging?
These days the trend is going to wards only one or two sources for 2ch audio, thanks to computers and media servers like the M1 Clic (of course, for multichannel, some might prefer a separate HD server or BluRay player from the gaming console). That means either the amp has a digital input as well (and of course its own DAC), or you have one DAC which takes digital input from several sources. In some cases, there's a good CDP on the analog input on the amp and a computer or other device on its USB or SPDIF input. The need for several sources is negated for example by a computer when it has both your music stored in lossless as well as access to internet radio (replacing the tuner). And despite the resurgence of vinyl, the newer hi-fi customers aren't all getting into it.
Besides it's not just the headphone amps that are trying to be minimalist - even speaker amps are following this trend of one or two inputs (one may be digital). Look at most of the T-amps and NuForce Icon. Even NAD's D3020 is minimalist in every sense of the term, unlike the previous amps that provided a full-spec preamp section and tape (loop) outputs.
What if you want to use it as a pre-amp for your speaker audio too? One input does not cut it and a remote would be much appreciated.
Some of these so called full size headphone amps are very expensive. A well known and respected manufacturer recently introduced one at the high end of the price scale. It has a wall wart PSU, a "Alps analogue volume potentiometer", 1 RCA input and a mini USB input. It seems like such a waste when all it would take to make this a truly functional pre amp would be to add a couple of RCA inputs and a remote.
Admittedly, to a lesser extent I can share your frustration on the lack of preamp functionality. However some amps aren't all that tiny but when you look at the board, at times size can be deceptive - adding more inputs and outputs on it would actually require the amp to be larger, or have a separate board for the RCA plugs, as old integrated amps used to. As for the price, well, every marketing and engineering team has a different take on what they think people need or want, so just don't buy those who got it wrong for you. My amp has one RCA input (waiting for my dedicated CDP or a DAC) and a USB input (which by the way sounds better on headphones than a lot of dedicated CDPs I tried) but the only thing I'm wishing it had was the preamp, which if I go for a DAC, will be a major requirement.
As for the remote, well, if it's dedicated for headphone use and perhaps if used for speakers than chances are it's nearfield, you won't really need the remote. I actually prefer knobs because I can switch the volume quickly just by twisting, as opposed to pressing a button one by one or squeezing it hoping to get the volume right before my ear drums are blown. That's a key convenience for me when you pass several source material from a computer (internet radio, podcast, YouTube, my own music, etc) through that device and into headphones. AudioGD by the way has remote models so you might want to check those out.
1. They want to sell you a pre amp AND a headphone amp.
Two things to remember: some really don't want to cram too many functions into the same chassis (more complex PSU, noise, etc etc), while others envision the DAC more as the receiver (as in a multichannel system) - or the hub - of the system nowadays given that most sources are assumed to output a digital signal into it as I outlined above. Take Meier Audio's designs for example - the DAC has the preamp (I think it even has an analog input that can be sent through the fixed and variable outputs) while the amp has as its only added feature aside from a gain switch a simpler crossfeed (that way, you can try it with any other source you hook up to the amp - CDP, TT, etc). That a computer and a more dedicated a music server can both go through the same circuit on this and sound the same (with the exception of source material that the computer has a wider variety available to it).
2. They only cater for desktop users who only need one input.
I personally would need one analog and one digital, and if I can only have one, I'd rather have digital. As much as I'm still planning to acquire a Cayin CDP in the future the reality is that needs of headphone systems tend to be very different. First off, the people who caused the boom in headphone audio in the past ten years tend to be younger - the "iPod generation" - who among many other reasons aren't used to getting up and swapping discs. Hence, a computer with all their audio in it plus internet radio and others has replaced the separate tuner and CDP. Second, even those who have are used to swapping out discs tend to have been frustrated in the past with the transport of their CDPs, and compare that to a touchscreen where you don't swap out discs, they can do the math and figure out where all this is going. Hence, the DAC as the hub (it might have its own headphone amp in it also that's good fro most headphones).
I've broken a number of transports before and it's just frustrating trying to get the parts outside the US. Belts would cost triple the price to ship here for example. Compare that to a touchscreen and having two options, plus a computer, in case one of them doesn't work. And when I upgrade my phone, I'll probably keep using my S3 as a music player. Regardless, these will all go into my amp's USB input, and if I really needed to hook it up to a speaker system, I'd probably use a DAC a preamp (again, the hub), or keep my headphone system out of the dedicated room for the speakers. This way I have my headphone system in the bedroom and a dedicated speaker system for when I'm doing nothing but listening. This doesn't mean that everyone else has exactly the same needs, but still, on the whole sources outputting digital (barring dedicated CD transports) are the trend nowadays, so multiple analog inputs (more than one or two) aren't likely to be popular in the future.
