@AudioThief
It is a little tuff question to address, especially considering the great bang for buck L300/SRM-252 you own now, but...there is a lot involved...and upgrading can be costly...
I would not get the Lambda Pro (and not sure which amp accompanies it), as at best it does exemplify the original Lambda presentation (attribute many like, I like both original & new) and first Lambda to exhibit good bass, but it also has quirky mid-range characteristics if you're into critical listening or some classical music, which may be bothersome. When paired with ED-1 (costly & sorta rare) it smoothed out the EQ finely (I have this combo) and then achieved its best, with that EQ function importance predominant over soundstaging effects. If the price of the Pro plus whichever amp is paired with it is really, really low, then it is an option, but likely will not get you past what you already have sonically.
Then, then bigger question is, the L700 and 007 are different in presentation, and half love one, the other half love the other, some enjoy both. But, both excel with as much amp as you can throw at them, especially 007. Plus there are a few versions of 007, so they are all good, but a tiny bit different (see Inexxon site translated for basic details). Any 007 will be above L300 as most also hear the upgrade with L700 also. But you will want to eventually move upward in amping to maximize their benefits. Others can chime in on T1/007 combo specifically. The 007 models and L700 may also reach their best potential with much different amps.
Plus, the 252 is SS and T1 is tubes, so there are other variables in the choices, and what you enjoy. The big question posed is how 007/T1 or L700/252 compare, which is hard to say for me, as have not heard the 007/T1 combo, but tend to think the 007 combo may synergise, not sure, if others can weigh in. The L700 & 007 both scale upward nicely with upgraded amps, yet there are some that have said they like L700 better than 007 flat out, so it depends on what you like. Most may choose 007 over L700. With both headphones properly amped to achieve their best, it's up to your preference in sound presentation, as Staxen goes.
Considering a used 007 & new L700 are close in dollars, the often overlooked factor is that a L700 can be driven with a moderate amp, but a 007 needs much more to excel and enjoy its potential. You actually can get away with driving a 007 with a SRM-717, as was the combo match some years ago & used mint 717 go for about a grand usd. Yet, they will sound better with more costly amps.
If we can get some others here to input on the 007 plus T1 combo, it can help you moreso. Either way, with L700 or 007, you are into handful, less than 10, of the best Stax. With either type, amping upward will get you there; but, the 2 hp's are different in presentation, so that is likely most important in what you like best. If the 007/T1 combo price is really great, it may be hard to turn down. As you said, amp upgrades are a future endeavor, so if the 007 alone is under a grand in good shape, it's a buy. Not leaning either way, the 007 & L700 present differently.
Hope of some help.
