Wirrunna

Go with 2" and suggest https://www.parts-express.com/prv-audio-adm25-50-1-3-8-18-tpi-driver-to-4-bolt-2-horn-adapter--294-2941 so the K55 and A-55G can be used. That's what I used with the 2" mdf Elliptrac.

What about the Eliptrac Horn - http://www.alkeng.com/trachorn.html and https://community.klipsch.com/index.php?/topic/144700-eliptrac-400-kit-finishing-update/&ct=1557489906 and https://community.klipsch.com/index.php?/topic/176161-what-happened-to-fastlane-audio/&ct=1576716864 for the email address. I have just finished building these and they are well worth the effort.

https://community.klipsch.com/index.php?/topic/164791-building-the-type-aa/

Type C schematic https://community.klipsch.com/index.php?/topic/113804-klipsch-crossovers/page/10/ last post on the page.

Dave, You are not exactly a newbie here so I won't insult you by asking basic questions, but apart from agreeing with glens the only thing that may be a help is this link to plans - which will enable you to compare the size of your splitter to a 1977 model.

There was some discussion in this link that ay be relevant - https://community.klipsch.com/index.php?/topic/177136-klipschorn-new-build-introduced-to-pilgrimage-attendees/

What size bolts did you use to fasten the adapter to the Elliptrac ?

Back in 1980, Audio Magazine published an article on Picking Capacitors - http://www.reliablecapacitors.com/oldRC/www.reliablecapacitors.com/pickcap.html While this article is primarily concerned with low level signals, the Summary is applicable to crossover circuits - "Above, 0.1 uF polypropylene (or metalized polypropylene) is the dielectric of choice".

Here is how to fix it -

A few years ago a story circulated in the Carriage Driving community in Australia supposedly told by a former Royal Equerry. It was about Ronald Reagan (who was an accomplished horseman) asking the Queen about the Royal carriages which resulted in the Queen inviting Ronnie for a ride in one of her carriages. The carriage driver (equerry) sat on the left hand leading horse of the two by two (four horse) team to ensure privacy for the royals and their passengers in the carriage. Ronnie's hearing aids didn't work well in the open air with all the horse noise and when one of the horses broke wind loudly and longly the queen apologized to Ronnie, who replied "What did you say?", the queen bellowed back "There are some things even the Queen of England cannot control", to which Ronnie replied "I'm surprised you said that, I thought it was the horse!"

Fair enough. I'll be interested to read how the Universal CSW crossovers sound in comparison. When I replaced the ALK Universals with ES networks in my K-Horns the imaging and clarity improved immensely (similar to having my ears flushed). I used REW as a guide to get the mid and high flat and then set my NAD C725BEE bass at 2 o'clock " to what sounds pleasing to my ears ". My listening SPL is similar yours.

How are you measuring this, can you do a sweep in REW to see what is going on ? I like to set the midrange level on the ALK crossover for a flat response via REW measurement as a starting point and then adjust via listening.

Alessio, have a chat to the Opening Poster of this thread https://community.klipsch.com/index.php?/topic/175660-la-scala-split-project/

Alessio, Have a wander around http://www.alkeng.com/ Also a couple of threads - https://community.klipsch.com/index.php?/topic/110366-why-is-the-alk-universal-network-universal/ https://community.klipsch.com/index.php?/topic/124362-alk-universal-crossover/ and maybe build one yourself - https://community.klipsch.com/index.php?/topic/164791-building-the-type-aa/

Disclaimer - I haven't bothered with TT technology for 30 years. The TT motors back in the day were mainly synchronous and relied on a constant mains frequency rather than voltage for their speed. The platter also used to be heavy to provide a fly wheel effect, especially when driven by an elastic belt. Technics used to build a turntable with a quartz crystal controlled ac power supply with extremely accurate frequency for their synchronous motor. So, in my opinion, a variac will not help TT speed fluctuations.