Pre-construction ceiling speakers

Its been awhile since this topic came up on this forum. What are people doing these days?
 
My new construction attic will have sprayed-on foam insulation and blown-in on top of it (Minnesota). Simply leaving ceiling speakers exposed in the attic won't work.
 
In searching for a back box I've come across the following: Backboxx, Eccobox, EZBarrier, and OEM Systems.
 
The OEM Systems vapor domes look like the best engineered product. But I've also discovered, to my great disappointment, that not all speakers are created equally when it comes to size. There is no standard for a 6.5" ceiling speaker opening size! I've not decided on a speaker but I'm thinking about Polk, JBL, Klipsch. The depths don't always work either (for example, JBL won't fit in EZBarrier).
 
I can't believe that nobody makes a universal ceiling speaker box and mud ring. ICAT (insulation contact air tight like light cans) rated. Fire rated option.

I recently tried these Tenmat cardboard back boxes, retrofit, for new ceiling speakers.  Not sure how they would hold up to spray - I would think they would be fine.
 
https://www.tenmatusa.com/insulation-protection-covers/
 
I bought 2 on Amazon.  They're like a heavy cardboard.  
 
I would ask the spray foam company owner for recs, if nobody has experience here.

Cut your own out of a board of 2" and let the foam guys go over it. Couple of coat hanger pieces to hold together while it's being sprayed.

Recently here DIY'd an OTA HD UHF antenna out of cardboard taping and gluing it together.  It was just an experiment to see if it would work and hold up in the attic.  (there is a regular OTA antenna in the attic).  I am still using it and just looked at it and it has held together just fine.
 
Personally I would make sure you have the wires run to the speaker locations.  I did this in a high ceiling great room using small rings with covers on them.  After home was finished I cut out the holes for the speakers (except that the insulation was dropped in the attic.  The insulation did fall from the ceiling and it was low on the WAF.  I just cleaned it up.  I used circular Polk speakers for the 7.1 wiring in the great room.  Helping a friend with his new home build here went to wall externally mounted speakers and just installed rings / wires / covers on the walls where the speakers would be externally mounted. 

I have other back boxes I made from MDF, and OSB.  If you have the time, DIY back boxes are dirt cheap.
 
I would decide on a speaker brand, and model now.  Then, build back boxes in the right locations.  
 
The easiest method is to turn the joist bay into a back box, with 3 pieces of wood.  I did that in my kitchen, with 8" in-ceilings.
 
I think the speaker pre-construction brackets are an added cost that could be skipped.  You're always limited to that one speaker size, as well (though ceiling speakers should last nearly forever).  Though, cutting the holes for the speakers is a littler easier, I would think, with the brackets.  

Here wife purchased one of those dremel tools with a vacuum attachment just for cutting drywall...but after I had done the ceilings in the family room here.   For symmetry here used those laser guide and pencil drawing on the ceiling.  I used the original architectural drawings to create a square in a rectangular room; then penciled up the ceiling a bit.  I did similar when installing the zoned audio speakers in rooms. 
 
As mentioned above just pre build your box out between the joists.  
 
Run the cable and take a picture of the location of the wires for the speakers or put in some mud rings (which is what I did and was low on the WAF).
 
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For anyone in the future with interest... I ended up buying something called EZ-Cap for my pre-construction bracket. Available from a couple of places including http://www.a1components.com/Products/EZ-Cap-Universal-In-Ceiling-Pre-Construction-Speaker-Bracket-(Each)__EZC1000.aspx. Be aware that the plug that is exposed is an ivory color.
 
I will probably use a Tenmat back box as a tradeoff between cost and time. The insulation contractor says they will be fine.