Dual Subs;Do i need minidsp 2x4?

hmm... other people will be around to answer but if you have dual subs w/ that processor then I think your good to go. Just level match them in the same place and run your tests from there on so they are sync'd.

I know my XMC-1 has built in dual sub management which will get used as soon as I order a second subwoofer.

First place them in the best position (using REW RTA) + set them up as mono.
Depending on your room generally one in middle of front and back walls or front 2 corners, experiment with RTA to determine this.
You want the EQ to do as little as possible, hence the positioning.
With 2 subs and the receiver you might be ok.
Before you take the plunge with the Mindsp or similar use what you already have.

Thanks Talley and Phillips,
So i guess minidsp 2x4 is only require if more than 2 subs?

The NANO AVR DL did a fantastic job with the dual subs in my clients system + the Dirac corrections in Impulse response were the best room corrections Ive heard so far....

I used a minidsp for two subs so I could send bass below the tuning point of my ported sub to my sealed sub.

With two SVS PB13u's and Audyssey xt32 you wont likely need anything else. xt32 is very good at tuning two subs plus the PB13u is very flat so the only issues would be in room placement.