do I need a mixer if I use Focusrite Scarlett

At the end of the day you’d still be sending out a 2-channel (stereo), or in a public venue like a stadium even mono, so anything that has stereo out already suffices.

However I would personally NEVER use such a mishmash of speakers for a gig like you are describing.

Also you fail to tell us what else you are using. Controller? CDJ/DJM combo? Laptop only?

On the PA-side of things, if it’s a big gig they are paying for the PA. In that case I’d get the right gear from a rental company and get the rental company to give you some kind of discount (I get between 10 and 25% discount depending on what I rent) while charging list price to the customer. That way you get to make some money, you can have the rental company bring and collect the gear and set/hook it up and take it down. And you will get suitable, professional grade gear (with all due respect some of the gear you mentioned is way below par and some is hit/miss acceptable, the EVs are a good set of speakers, all imho) with a guarantee it all works.
Also, you can tell them what the field looks like, the kind of music/show, the amount of people that are expected and their dispersion and they will be able to advise you exactly as to what gear and what setup will work best.

All you would need to do is plug in either stereo or mono (mono would be my guess and choice) from whatever you are using (something we can’t answer yet due to a lack of information).

On a general note: for outdoor use you should calculate about 10 Watt RMS per person, provided they are relatively close to and centered around the speakers. RMS is something else than a lot of manufacturers write in their brochures! There they usually use terms like PPP (peak program power), pmp (peak music power) or other euphemisms to disguise the true RMS values. The 10W/person is based on an average sound pressure level. If you want really loud or extra heavy (sub)bass for example, this number could go up substantially.

Maybe not the answer you were looking for, but just my three cents as usual.

Can’t get the rental company to sponsor the fundraiser? 😀

You have two XDJ1000s?, what mixer?

And you are sending the identical stereo sound to all the outputs on the FR?

Can you set latency on the individual outputs?

On a more general note:

If you want to bring sound to a large area, without a clear front/left/right setup (i.e. crowd can be anywhere, facing any direction), it pays to go mono. For this your mixer, controller and/or DJ software needs to be able to deliver a mono signal. Sometimes your sound card (if you use an external one) will have a stereo mono switch. At that point you only need 1 channel of output. If you are using balanced cables there is no need to have several source signals, you can just daisy-chain all your speakers.

The only exception here would be that you would want to go to any subwoofers first (provided they have built-in cross-over and a high-pass out connector) and from there daisy-chain all other speakers if you want only the sub to do the super low, otherwise just link the subwoofer anywhere in the chain, but be sure to use the “through” connector to get full range signal to any speakers further down the chain.

Do yourself and the event a favor and rent a PA.

Have them rent the gear and donate your DJ skills to support the cause.

I just checked the sub (1800X Pro) and it isn’t powered as you stated in the OP! That means you have another amp for the subwoofer? And an active crossover? Suddenly this becomes a much more complicated setup as you need to start thinking about how to split the frequencies for proper use of the sub and other speakers.

While perhaps disheartening, it seems you – unfortunately – don’t really have the proper gear to – easily – take on this task. It happens.

Interesting discussion. I’ve just ‘upgraded’ to a Focusrite Scarlett 6i6 from an M-Audio Fast-Track Pro, and was disappointed that the 6i6 does not have the mono switch that the Fast-Track does. Mono is best for fields etc. – in the past I did gigs for decades at such events, and used 100v line connected loudspeakers to get the coverage. The best advice is to test it first, or hire in the PA. Nevertheless, if your event crowd is based on one corner of the field, the kit you have, suitably protected from the weather, might well work OK. The crowd will draw closer for volume if that’s what they want, others will move further out. Test it all out in a similar situation first.

And test it all out well in advance.

Also, the Rockville (8 Ohm) and 2x Behringer (4 Ohm) combined on the amp will give impedance mismatch, a situation you don’t want.

The Rockville is the type of thing we warn people here not to buy. It’s total and utter (sorry to say) crap. For the price of a complete cabinet with damping material, passive crossover and a total of 6! drivers, including 2x 12″ costs about as much as one DIY Celestion 12″ driver. You can do the math. It can not and will not sound even halfway decent. It’s a nice thing for a kids bedroom and will look impressive at his/her birthday party in dad’s garage, but nobody that wants to be taken even remotely serious as a DJ should want to bring that piece of gear to any public performance.

So, taking the Rockville out of the equation, you could do the following, still employ most of your gear and get as close as is possible to achieving what you want.

1) Imagine a square or elongated “dance floor” in front of the DJ Booth.
2) Put the sub/qsc combo left or right of the DJ Booth to provide sound to those right in front of you. Best would be to get one extra qsc on a stand, so you can have tops on either side of the booth.
3) Put the EV’s on the near left and right corners. If you have a second qsc you CAN put the EV’s a bit further downfield aiming them towards the middle.
4) Put the Behringers on the far left and right corners. Here you can either choose to aim them back at the middle of the “dance floor” or aim them further downfield, depending on the area you want to cover. Beware that there can be an audible delay if you put them too far away.

It’s the only way I can see this mishmash of gear coming together in some sort of coordinated fashion.
But please leave the Rockville at home (frankly, just sell it off and get a second QSC for example).

In this setup, be sure to go to your sub first and connect everything else from the sub output (not the sub-through!). Since the amp has no through connectors, it needs to sit last in the chain.