I'm currently using my Lenovo Thinkpad 2 as a portable audio device. It has a duo-core Atom processor and comes with a full size USB port and a microSD slot that supports 64GB cards, so it easily fulfill my needs rather well.
The processor is fine for PCM when I use it with my Meridian Explorer but underpowered for DSD -> PCM on the machine. However, when I use the iDSD nano from iFI, it plays everything properly, all the way until DXD and DSD128.
To me, the Thinkpad 2 is near its EOL so I'm looking at the next gen machines. The new lower cost consumer tablet from Lenovo is the Ideapad Miix 2 10.1 (not the 11 inch) which uses a quad core Atom processor (Z3xxx atom processor); the 11 inch unit uses an i5 processor instead.