I spent some time with the 990's headphone jack over this weekend. Grado SR80, Senn HD580, and Ety ER4S were headphones that I tried. First of all, over the two channel music materials, it sounded fairly decent but nothing like having an headphone amp to drive the headphones. The highs were rather soft and little muddy sound. Mid range and bass seemed like all bunched up together without clear distinction among instruments. However, out of three headphones, I prefer HD580 to be most pleasing over others. The sound coming off Ety ER4S was harsh and very thin sounding. I guess I am used to listen to my headphones using quality separate headphone amp for musics. If you have never had a chance to use separate headphone amp, 990's headphone jack is par with other receivers, pre/pros that I used before. Although nature of Dolby processing gave little more wide sound stage, I still prefered to listen in two channel unprocessed sound of headphone. However, Headroom amp's (www.headphone.com) internal crossfeed circuit can be wonderful sounding on various music sources if you like those kinds of music processing. It is not same as cheap gimmicky sound of DSP (likes of jazz room, stadium, concert halls, etc....).

However, when I put the DVD movies for listen with the headphone, it simulated very decent movie soundstages with real sense of surround effects and directionality. True that I prefer watching movies with external speakers setup but if it is between listening at very lower volume externally vs. headphone at decent volume, I will take this Dolby headphone anytime. I used to use Sennheiser DSP Pro headphone processor for my late movie watching which I still do in my other two channel system but with the inclusion of Dolby headphone processing in 990, I tend to use its feature at late night viewing in my main HT system more often. If I am listening to two channel music only, I prefer to use my separate headphone amp portable rig. But if you don't own separate headphone amp, 990's inclusion of Dolby headphone processing will be welcome feature. BTW, separate headphone amp will bring out the full potential of many quality headphones out there but with not-so "good" quality cheap headphones will benefit very little sound improvement. So in my 990 system, the only time that I use its Dolby headphone feature is watching movies at late night. Again, this inclusion of Dolby headphone processing feature in 990 wasn't the deal breaker for me but it shows what an incredible bargain 990 really is. Outlaw design/research team really did a nice job bringing us one of the best full featured pre/pro out there.