This is from one of my posts concerning the mp809t at needrom, I don't know what problem you had when using vroot, but maybe this could help:
For those interested in rooting this version (kitkat 4.4.2) for the 6592/2G/16G phone, I did it using the next steps:
1. Apply the vroot method from your pc
[Only registered and activated users can see links Click here to register]. It will not fully work as the installed supersu will not work. Installing a supersu afterwards from playstore won't work either, however your phone is "patched" to root.
2. Get the 4.3.0 rom from the great needrom here:
[Only registered and activated users can see links Click here to register]
3. Do not install the complete rom, ONLY the recovery.img and nothing else using the normal steps with flashtool.
4. Get the supersu toolkit from here:
[Only registered and activated users can see links Click here to register]
5. Rename the file to update.zip and put it on your sd-card (the external).
6. With the card in the phone restart into recovery (vol + and power hold). This will get you into cwm recovery.
7. Go to the install zip from sdcard, and apply udate from sdcard, execute it and reboot your phone normally
8. It will update your apps and after that your phone will be rooted. Check it with Rootchecker
[Only registered and activated users can see links Click here to register] When you start this app supersu should popup to ask for root permission.
9. Install busybox from playstore:
[Only registered and activated users can see links Click here to register]
10. You're done, now you can enjoy your rooted kitkat.
NOTE:
In your case step 2 is not to be applied as that rom is for the 809t not the mini, you'll need to find an apropiate recovery for your phone. If you can't find it you can make it yourself by using droidtools and flashtools. The way to do that (in a nutshell) is make/get a scatter file, do a readback with flashtools of a large part of your rom, then you use that file in droidtools to create the cwm modified recovery which you can flash back with flashtools.
Hope this may be of use.