I have taken a post from our Facebook page, outlining the upgrades to the CX/EX
The case work is not changed. The main board is retuned and the CX board gets new/more RAM. The power supply and control electronics are completely replaced. Good sounding fuses are installed. New software is installed. You get the benefits of a lot of design work needed in order to make these upgrades worthwhile. We cover express courier freight and all border processes and costs for most countries - there are some exceptions, where the customer will need to deal with border costs.
In terms of sound quality, the K50 is a large improvement over the CX+EX combination.
The upgrades close around 80% to 90% of that gap (on USB). I am stating a range of percentages because it is impossible to be precise when peoples’ systems and preferences are different. We have a long history of offering to keep peoples’ older units up with our latest technology and we don’t offer upgrades unless the sound quality improvement will be very significant.