"HOLD" her up there cdc2 !
The root of the problem with your present system lays with the amp you’ve chosen to drive a 4 Ohm electrostatic speaker that’s 92dB efficient.
MartinLogan suggest using up to 500 watts of power to drive these speakers, you’re using a 70 watt Tube amp & you’re wondering why your system lacks dynamics in a room that’s 30ft long?
Before ditching the Marty’s get a hold of a 200 watt into 8 Ohm/ 400 watt into 4 Ohm SS amp, (borrow it for a week or 2) . A Threshold, a Krell, Sim Moon, Mark Levinson, what ever, just a good quality amp with lots of headroom. That will rectify your dynamics problem and more.
As for the sound stage? I heard the Ethos driven by Sim Audio separates in London, my only reaction was - wow ..... I also heard the bigger predecessor of Ethos driven with lower powered Naim separates and with a Krell KAV-400xi integrated amp. Driven by the KAV-400xi the Marty’s were in another league altogether than when played with the Nain stuff.
You’ve also got your equipment selection path back to front.
If you’re dead set on switching back to speakers with conventional drivers, that’s where your Prima monos will shine, but even then I’d look for a speaker that’s "more" efficient than the 91db Gibbon Super 9’s in a 30ft long room with that amp. (That’s no knock to the Gibbon’s).
A caveat in closing, by their nature skinny speakers are hard to drive, so that reduces the elasticity of your Prologue Sevens. Now if you were looking at a pair of Klipsch Horns the Prima’s would be the bee’s knees.
Here’s the two solutions I suggest, stick with a Tube pre-amp (if that’s what you have), and ditch the PrimaLuna. It’s a really nice amp, but it just isn’t conducive with the application you seak, either your MartinLogan’s, or a skinny dynamic speaker, or a 18’X30’ foot room.
#1: Get a good SS amp as I suggested above to go with a Tube pre-amp and keep your MartinLogan’s.
#2: Get a skinny, inefficient conventional speaker, such as a used PMC Fact 12, Focal Electra 1028 Be, Vienna Acoustics, the Gibbon Super 9’s, stick with a Tube pre-amp, and drive your speakers with a 200watt ANTIQUE SOUND LAB HURRICANE amp.
Hope this helps & enjoy the music.