High pass filter capacitors

     It's been decades, but- when I needed high quality, small value caps, for doing exactly what you are (using a Placette and/or Dahlquist DQ-LP1): Michael Percy was my go-to, for the best parts available.

                    He also offered a wealth of valuable information.

                            Can't even swear if he's still in business.

                                                     BUT:

                            https://www.percyaudio.com/Catalog.pdf

                                              Happy listening!

In this range of capacitors, there are a number of excellent brands of caps for far less than $300.

Audyn TruCopper, and even some excellent Duelund models like this one.

I strongly recommend you practice however using like $2 poly caps first, just to make sure you have the right values and wiring.

Also, I think Parts Express has some modular XLR adapters.  They are like M to F adapters but you can shove little parts inside. Perfect for this type of prototyping.

I’ve look at the vcaps. I’d need 4 on XLR lines. 😫$$

gdaddy1

Thanks for the video. I haven’t seen that one. 
I’m hoping this is not the case here. 
Danny Richie designed these speakers and suggests to do this if playing at louder levels. 
I have them with an AV processor with its internal crossover cutting the lows to the bookshelf speakers. They sound amazing to me. Very deep and wide sound stage. 
My plans are to upgrade to a BHK pre used in bypass for the AV system. 
This will require a filter on the pre output. 
Any suggestions welcome. 
I will check out the Miflex caps   Thank you. 

Why are you doing this?
 

I have GR Research NX Studios. (Bookshelf)

They can’t handle below 70 hz. 

If the goal is to "Remove the main speaker woofer work" this mod will probably do more harm than good. Especially adding phase shift to the upper frequencies. This affects the imaging and soundstage as well.

Paul McGowen discusses in this video.

https://www.youtube.com/watch?v=nmZTXn2NHLY

If you're willing to spend more (unfortunately considerably more), many consider the VCap CuTF the best sounding audio cap available. 

Why are you doing this?

I'd recommend the Miflex KPCU-03. Very nice sounding cap. I've used it for this same purpose.