Let's back up a step -- I thought you were buying speakers for a new setup, and I didn't realize you already had a complete 5.1 setup currently. So let me ask, after calibrating with the 818, what do YOU find lacking currently? What are you trying to upgrade exactly? Do you just want to expand with more speakers (i.e. wides and a surround back) to take advantage of the capabilities of your receiver? If you are happy with the V-Mini's as currently setup, I would just keep rolling with it.
Do you have any issues with the current asymmetry? It looks like the screen is off center to the right, and the left front speakers is spread wider than the right?
Just as a side note, given the 17ft distance it's going to be tough to meet the exact DSX angle specifications for the speakers. Is there any way you can get a bit closer to the screen? For example, playing around with an online trig calculator, if you placed the new L/R speakers just outside the edge of the PJ screen, they'd be about 8-9 feet apart. Even generously giving them a 10ft spread, that only works out to a +/- 16 degree separation on the front mains at 17ft.
Even if you placed them slightly forward of the screen so you had, say, a 15 foot distance from the plane of the speakers to the listening position, that's about a +/- 18 degree spread. Basically, I wouldn't place them that much narrower than you currently have them set, and then you'd have to bring the "wide" speakers forward quite a bit to get close to the recommended 60 degree +/- spacing. Obvioulsy you don't have to be exactly perfect, but ideally you could get within 10 degrees or so of the recommendations. If you intend to move them forward as "wides", assuming a 15 foot separation laterally, you'd probably want them to be at minimum half-way between you and the screen in terms of the length dimension (i.e. maybe 7 feet forward and 7-8 feet out to each side).
Be aware that DT is notoriously generous in their freq response specs. They don't actually quote the standard -3dB spec as do most other manufacturers, most think it's the -10dB point or some other measure of absolute "usable" response. They call it "total frequency response" but who knows that that actually means. The PC 1000 has 4.5" woofers like the Energy V-Mini's, there is NO WAY that they can produce usable bass down into the 40's, let alone below the 80's.
Well, I guess it all depends on how picky you are. Based on my experience they aren't DRAMATICALLY different, but they are different enough that I wouldn't want to mix and match across the front soundstage. They'd probably be fine for example to mix front with surrounds, but the coherence of the front speakers is pretty important for seamless immersion. So unless you have to I'd rather stick to one brand if possible.