There was a time when you could source a D2000 for 15-16k or so and for those price it used to be really awesome . Now the prices have shot up and you would be lucky to find it for anything less than 19-20k
. I dont think they are worth that price tag.
For 20k , you are better off buying a Beyerdynamic DT880 Pro from #PrisitneNote . They are also official distributors for Fiio so you can contact them .
If you want the D2000 only , then I would suggest you pick up the one's Metalspree has offered you . I myself have tried out the MarkL mods on my D5000 and also the same upgrade cable which Metalspree has - I can tell you the overall sound is way more controlled and detailed compared to the stock D2000.
The E7 will be decent for the D2000 , but not the best . If you plan to use it only with desktop I would suggest you get the Fiio E10. If you can spend a little higher look at the Audinist HUD-MX1 .
If you need for laptop + mp3 player both then E7 is your best bet in a budget since it acts as DAC (soundcard) + portable amplifier for mp3 player.
Actually you might not really notice a lot of difference with higher end sound cards , so don't bother until you try it out .