spatial audio M3 or M4 as an upgrade

I am using a pair of rebuilt and fully modded pair of dahlquist  dq 20s.All internal caps,resistors,wiring,inductors,posts upgraded.also used a product called cascade in woofer cabinent .cascade is like concrete when dried making cabinent dead.Silver  solder brass screws and more used.I am considering An upgrade.Can anyone chime in about spatial as an upgrade and not a lateral move?It It's hard to go back to a box speaker after these.I want to dethrown these at an affordable price.I want music to sound right and be able to hear subtleties at same time.It 's hard to get the brass right and hear the details too.
Hi Rick,
I have had the M4 Turbo S speakers for about 6 weeks after having Linkwitz LXmini's and I am delighted with these speakers, but I can't give you a frame of reference to your Dahlquists.  After having had box speakers for over 45 years, these are pure magic.  I  got the M4's for the size of them, being located within 3' of back wall and they perform very well.  They have a much wider sweet spot than planar speakers and go pretty low.  Overall, they are quite neutral in sound., and have excellent HF extension and inner detail  They sound sublime with tube amplification, and quick and controlled with my Conrad Johnson MF80 SS amp, tho they give up a bit of the warmth and liquidity with the SS amp compared to the tube amp, but are somewhat better controlled.  Clayton Shaw is a brilliant  designer who has incorporated a lot of SOTA technology into these speakers.  Selling direct more or less halves the price of speakers sold through dealers.  

Here are my recommendations:
1.  If you have the room, go with the M3's over the M4.  The M4's go to 45hz and the M3's got to 32z, quite a difference.  The LF is pretty much the only difference between the two.  If you have a sub, the M4's will be fine.
2.  Opt for the Turbo S version of either speaker.  The tweeter design is more robust and the internal wiring is far better.  I didn't compare the two, but others have concluded the $500 upgrade is worth the expense.

I have have had several audio pals over to hear these speakers and they have universally been pleased with their performance.  The fit and finish is top notch and one guy thought they looked very modern and elegant.   I got think they sound their best with tube amps, but that is personal preference.   Good luck, Mark 
I am using a vandersteen sub that blends well with many speakers.My only concerns are the m4 sitting so low.I keep leaning toward the taller speaker due to tweeter height.I have 100 wpc ss monoblocks that are very open and accurate.I also have a BAT preamp with adjustable gain to keep all sources at same vol. level.I don't know if this will offset any hiss/noise etc.At my current 86 or so db efficiency I don't have a problem.I also don't know how my room size will change When i relocate in the near future.11 x 24 is current room size with open doorway at rear.I am about 4' or so in the room due to entry door behind speakers on side wall.Last set up was in large basement with low ceiling.Any thoughts on hiss and height?Rick
Thank you for the detail analysis on the Spatial M4. I presently have a CS 3.0 MkII setup and driving the same with a Woo WA5 Set Class 300b 8W high current amp. that is the best I have heard from the speakers and personally have tried many SS amps and found the Woo best. The closest that came to it was a First Watt F1. Hard to beat the warm tubes sound, mids and highs to kill for, especially 300b. I am now wanting to try the Spatial M3 full range passive crossover setup. I presently use the CS 3.0 MKII with a JL 113 for LF but I feel the combination is not the same having the woofer matching the envelope incorporating from one chassis.