I've always dreamed of a simple life, where one headphone, one amp, one DAC, one cable, will suffice. Alas, it's never meant to be. You see, in the Air Force, they have what is known as Multirole Fighter, much like the F-35 Lightning and its variants. Oh, I'm sure the top brass would love to have it simple as well by creating these multirole fighters. They dreamed of a day where there will be only one type of fighter for all kind of missions: dogfighting, striking, bombing, ground supporting, long range interdicting, intercepting, AWACS killer, and it's not just the Americans: Russians have Su-35 and Mig-35, The Swedes have the Gripen, the French have the Rafales. the Chinese have the J-10B and the J-16. However, the problem with designing these type of aircraft is you might end up with a good plane instead of a very good plane for the missions it is intended to do. Take the F-35 for example, I've heard that it is plagued with inefficiencies and compromises. For example, the Marine version have a lift jet for VSTOL operation at Forward Airbases, but the Air Force version ended up with a huge gaping gap where the lift jet would be in the Marine version (AF version don't need the lift jets, they can take off from proper runways in proper airbases), due to the common airframe they must share. When you pit it against other airplanes, the combination of stealth, electronics, and radar systems will score it multiple victories in real battle, although a Sukhoi Su-35 will outmanouvre it in a dogfight, and it is nothing compared to the payload a B-52 can carry in a bombing run. According to the planners, this is what F-35 supposed to do despite the aforementioned problems. This is why we won't be seeing the Air Force retiring the A-10, EF-18, B-52, and F-22 anytime soon despite the multiple capability of the F-35. Same thing also happened with headphones, many headphone manufacturers fall into trap of trying to be everything for everybody and ended up pleasing no one.

I am pleased to say that the NAD Viso HP50 is a rare breed of multirole products that is good in all aspects, while being excellent in some. It's excellent plugged into my Burson HA-160D and my Objective2. It is good plugged into my portable gears, and even straight out of my iPhone 5S, which means you can use it for both portable and un-portable applications with great results. Other reviewers more experienced than I have stated what this headphone sounds like: It has a full bodied mids, slightly boosted bass, and an inoffensive treble. I'd say it follows similar signature as many other newer European offerings from Philips Fidelio ranges, Momentums, B&O H series, B&W P series, and Focal Spirit series, but with even more careful tuning and refinement. This kind of signature suits multiple genre of music, apparently. I think Paul Barton did superbly in the tuning and the refining of this headphone. If you can only have one headphone, this is what you should get. This, IMHO, is the F-35 of the headphone world

I have always loved the Grado RA1 which uses the high output NJM4556 op amp. It was one of my very first introduction to the world of headphone amping, and for years it was the mainstay of my main listening rig, both desktop and portable. The JDS O2 amplifier is using similar op amp(s) for its output stage ( and doubles it!), thus I found this JDS Labs Objective2 amp to be easily lovable right from the first listen. It does bear a resemblance in sound to the RA1, but it has more definition, cleaner sound, and more power as well.

I had owned a lot of affordable amps: the various CMoys ( I have owned most major CMoy version:JDS, Zigis, Penguin Coffee Amp), 3 Channel PIMETA, Schiit Magni, RSA Shadow, XCan V2, GSP Slee Solo mk2, RA1, PA2V2, Creek OBH11 amp, and Fiio E12, but the time had come to downsize the number of my amps. I sold the others (I need the money to get an iPhone 5S, which is unsubsidized in my country's market) and kept the O2 as my one and only one amp after months of evaluating them side by side. It came down to these three: Schiit Magni, RSA Shadow, and JDS Labs Objective2, and then I picked the O2 out of those three. I haven't regretted my decision ever since;  I very much enjoy listening to Smooth Jazzes, the likes of Lee Ritenour, Earl Klugh, Fourplay, David Benoit, Dave Grusin, Incognito, etc. with this amplifier. It's paired with the following: AKG K702, Audio Technica ATH CKS1000, Philips Fidelio S2, or VSonic GR07 mk2, and also with the ODAC, Rockboxed Sansa ClipZip or the iPod with DIY iMod as the source. I love how the amp effortlessly disappear allowing me to enjoy just the music.