The Meier Audio Corda Stepdance is a portable amplifier - it is not a DAC + amplifier. It has been discontinued, but can be purchased used.
The Meier Audio Corda 2Stepdance is a portable amplifier - it is not a DAC + amplifier. It is still in production.
The Meier Audio Corda Quickstep is a portable amplifier - it is not a DAC + amplifier. It is an RF-shielded version of the 2Stepdance for those who might suffer interference when using a wireless phone in close proximity to the amplifier. It also has heavy-duty jacks, and is still in production.
The amplifiers, above, must all be fed with a line-level analog signal from your choice of source devices.
The Meier Audio Corda PCStep is a portable USB DAC + amplifier. It has both a DAC and a somewhat compromised (in my opinion) version of the Quickstep amplifier, all in a case that is the same size as the Quickstep.
Per your comment, let me explain that USB DACs allow you to use a PC, laptop, MAC, or Linux machine (varies with the DAC), as a transport for your music files. You plug the DAC (or DAC+amp) into an available USB port and then use software like Foobar 2000, WinAmp, JRiver, Amarro, etc. to play the music. The DAC intercepts signals that would otherwise go to the PC or laptop speakers, routing them instead to your amp and headphones - offering much improved sound quality vs. plugging the headphones directly into the sound card jack of your computer. (That was an oversimplification, but I hope it helps.)
The CEntrance DACmini CX is a DAC + amplifier that was not designed to be portable - it's essentially for desktop use, and supports four possible inputs: USB, Toslink (optical digital), Coaxial (wired digital), and Analog (line level).
I mentioned the DACmini CX only because it's recognized as doing a great job and having good synergy with the Audeze LCD-2, and in my opinion, as previously stated, it's really hard to distinguish the sound of the well-respected DACmini CX from that of the well-respected Stepdance amplifier (when the Stepdance is supplied with 15-Volt DC external power, instead of 9-Volt DC internal battery power).
So, I was NOT suggesting that you buy a Stepdance -AND- a DACmini CX.
I was just saying that the Stepdance is a surprisingly good amp for the LCD-2 - the equal of a DACmini CX - and that I have personal experience using the Stepdance with both of the headphones you mentioned - the Ultrasone Pro 900 and the Audeze LCD-2.
I don't know what you are currently using as your transport (the thing on which your music files reside), but you can start out buying just a portable amplifier, like the 2Stepdance or the Quickstep. A DAC can be purchased later, unless you currently have a need to use a laptop or PC as your transport.