...These headphone are truly unique and I can only imagine the benefits of going up the ladder into the Stax lineup.
You are in for a big disappointment - if you like L300's sound signature, there is nothing below 009 that will make you happy.
L300LE, L500, L700, 007MK2 all lack the ethereal highs, and L700/007 may sound quite colored in the mids, losing the transparency for which electrostatic drivers are famous.
You can get yourself L500 for just 100$ - the only difference between L300 and L500 that affects SQ is the pads, and you can buy them for 100$ -
https://www.headamp.com/products/stax-ep-l500-replacement-earpads-for-sr-l500-earspeakers
They will significantly improve bass response, but will eliminate the magical highs...
Hey
@BenF @DecentLevi I just posted this question in the Stax thread, but thought I could ask you directly.
I've had my L300 for close to a week now and only today I noticed a little popping sound on both sides when turning the SRM-252S energizer off. Is this to be expected?
A few months ago I switched jobs, and the new job didn't have enough storage space in the office for me to have all my favorite headphones/amps...
So I had to make some difficult decisions, and ended up packing my entire electrostatic collection (6 headphones + 4 amps) into a 120 liter plastic box and moving it to my storage unit... I even had to throw out the fifth amp, as it didn't fit in the box

Takstar Pro 82 v2 won this war quite easily - it sounds almost identical to 009 (when used with certain synergy combos), and it's much better suited to office use, as it is a closed headphone with excellent passive isolation. I was using Pro 82 v2 about 90-95% of the time before anyway, so it was an easy decision.
So now I can't test my 252/253, but I think a quiet popping sound is something I may have encountered myself.
...For context, I'm using a Jameco 12v power adapter with a reverse polarity plug, if it helps.
I don't think it's related.
Still, I would recommend purchasing a proper LPS. Even if I'm not sure I could tell LPS from a Stax adapter in a blind test, knowing that I am providing the best power input possible makes it easier for me to relax and enjoy the music.