The HEARO 999 transmitter base without the wireless headphones would have limited uses. The wired headphone amp is very good as it was made for inefficient AKG pro headphones. My K601 headphones sound better through the HEARO 999 than anything else they have been driven by. No surprise, as AKG would have voiced the amp for their headphones. The K601 driven by the internal amp and the wireless headphones sound almost exactly the same when you compare the sound. The K601 is much lighter, so better to wear those when near the transmitter base.
The DAC in the HEARO 999 is very good, so a recording engineer on location could always use the internal DAC and not have to depend on something unfamiliar. I use the DAC in my home theater setup as I feel it is bettr than the one in the CD/DVD player, and I use the coaxial input, but it has a switchable optical input.
Make sure you get the nice foam lined hardcase, recharger, leather earpads, and full owner's manual. The headphones could monitor 3 different transmitter bases, so they are different than consumer headphones. The primary market for the HEARO 999 was the pro market, but a lot of consumers would be better off with pro gear at times. You can have 3 transmitters running at the same time, and monitor different things. For instance, a microphone and tramsmitter in a child's room, the news and weather from a tuner at specific times, etc.
These were closed out, the complete setup, for $449 from 8th Street Music back in 2007. Extra headsets were $200. I should have bought two of the complete setups for $449 each. The extra DAC and headphone amp was worth the difference.
With the addition of a switchbox, the transmitter base becomes a full fledged line level preamp. It has an analog input and a variable output. With the addition of a small phono preamp in the switchbox, a vinyl addict would be well served as well. With the addition of a sine wave inverter and battery pack, you can go fully portable with the HEARO 999.....or get off the noisy and dangerous electrical grid.
Grundig makes some Yachtboy FM stereo tuners that would go well with the HEARO 999. Old school FM tuners can't handle the cell phone interference that is pervasive today. A small Yachtboy can actually outperform audiophile tuners of the 70's and 80's in a noisy environment, which is anywhere in a populated area.