Build or buy, speaker options

I have a pair of Triangle Volante 260 speakers which I love dearly most of the time. The times that don’t love them dearly are the Fridays when I get home from work and want to shed the stress of the week with a little high energy wall of sound type tunes. As mentioned before in this forum, the midrange and high end quickly fade out after a short while at high volume, then fade back in when I turn the volume down. Georgehifi posited that it could be iron core inductors in the crossovers getting saturated, and that sounded feasible. But, in an email conversation with Madisound, their tech indicated that he’d never experienced such a behavior, and that saturated inductors were more likely to exhibit distortion. The tech ask for some photos of the crossover, but I wasn’t able to get a clear shot of one of them, and trying to remove one from the cabinet proved much more involved than I thought it would. No good photos, but I did see iron core inductors, for sure. The Madisound tech thought “Maybe they are using poly switches that close when the power is too high, putting the speakers through a resistor”.  This is something I’ve never heard of, so I’m totally unfamiliar with poly switches or what they might look like.  It’s looking like I may not be able to solve this problem. 

The options I’m considering are selling the Triangles, and purchasing used market speakers, or building my dream speakers.  

If purchasing used, the qualities I like in a speaker are: detail, frequency balanced but leaning slightly toward warmth, tight punchy bass with authority, and higher frequencies that are truthful and never screeching. They would also need to handle a fair amount of SPL without strain. Amplifiers are Parasound JC 1’s.

If making my own, I’d be shooting for the same qualities. With that in mind, I’m considering a sealed cabinet design for two 8” woofers.  Separate cabinets for midrange and tweeters, also sealed. I think I’ve decided on the drivers for the bass cabinets, the Morel CAW938 9" Woofer, which is an excellent driver for sealed design. The midrange, I’m considering either one or two drivers per cabinet, the reason for two would be power handling, although I’m also thinking that this may be overkill, and that one driver per, with good power handling may be the ticket. Manufacturers I’m considering for midrange are Morel, Seas, and ScanSpeak. Tweeters are yet another big question, but the more I research the topic, the more I lean toward soft domes, same manufacturers as the midrange. 

Crossovers are yet another War and Peace length set of considerations,  but I am thinking about active crossover between the bass cabinets and the mid/tweeter cabinets, a passive crossover between the mids/tweeters. Amps for the bass cabinets would be newly acquired D class, possibly in the 500 wpc range. I’d use the JC’s for the mid/tweeters cabinets. 

I’d be interested in any advice, comments, experiences of others, as long as they aren’t overtly rude.  Budget for either purchased or built would be in the $4000-$6000 range.  

And, I’ve been following with interest a thread on this forum regarding the merits/drawbacks of sealed and ported systems. Some interesting observations and opinions. 

@ dprincipato 
Sorry,  I just came back to this thread after a couple of days.  Most good designers use air when at all possible.  Occasionally,  a core is a must because of DCR.  A Steel laminated core will not saturate as fast as iron ferrite.  The problem is if you measure DCR on an air core of any value, you might have 2 to 4 ohms,  when you measure DCR on a good Steel Laminate core,  it is more like .2 ohms.... when you replace the coil and add the extra resistance, it is very likely that you would reek a bit of havoc with your crossover.   I have a few of the best steel laminated core coils that I have ever seen,  they measure about 2.1mh and are a .13 DCR,  they are a 14gauge magnet wire..... If you can get a measurement of your current coil,  I could send you a couple of these to replace.  If you are not experienced in crossover work,  I recommend leaving it alone.  What part of the country are you in?
I have owned Acoustat 2+2 electrostatics, Maggies, three way Dynaudio d'Appolito towers among other store bought speakers while at the same time I have been designing and building DIY speakers for the last forty-seven years.  My first DIY project was a sonic disaster, but I enjoyed the process so much I kept at it. 

Before the internet I studied every book on speaker design and construction I could find, ordered reprints of AES papers, etc.  Needless to say with the internet information on the subject is available from a near endless variety of sources.
In 2004 I started sawing wood, machining brass and bronze, buying components, etc. to build my present triamplified fully horn loaded DSP controlled speakers.  I finally finished them up in their present very satisfying form in 2017.  Along the way I changed two pair of the drivers, the DSP unit, the bass horns and other components.  If at first you don't succeed ................  Also there was a huge amount of labor involved.

I didn't build DIY speakers to save money, but instead to have speakers that sounded and looked as I wanted them to.  I have come gratifyingly close to that ideal.  Also very gratifying is the fact that audiophile fiends who have heard them use superlatives to describe the sound.
If anyone is interested a description and photo of the speakers may be found at: down the page to the post by Don Reid (me).

Excellent drivers, good wiring, absolutely solid resonance free boxes (easily built for in home listening levels), and a DEQX machine, and you probably have it made, 
. Georgehifi posited that it could be iron core inductors in the crossovers getting saturated,

Iron core get saturated very quickly, like, immediately, and the measurements I've seen show the distortion is relatively low when it happens.  What it sounds like you are suffering from ins normal driver thermal compression, and the distortion here is rather high. 

I'm a big fan of DIY, but maybe what you really need is a high efficiency speaker system? The low wattage tends to minimize thermal compression effects, and a compression driver will minimize doppler and IM distortions.  Maybe the Klipsch Heresy is what you need??