I just saw a bunch of videos where they were talking about pre amps and running dacs off amps etc etc.
Not sure what you mean by "running DACs off amps etc" - the Digital to Analogue Converter takes a Digital signal and then Converts it to Analogue, then that is passed to the preamp stage to control the signal strength either by boosting it (as on an active preamp circuit) or attenuating it (on a passive circuit), then it gets passed to the final amp output stage which really amplifies it to a stronger signal that can move a transducer (ie a headphone driver or speaker drivers like midwoofers and tweeters).
These circuits can all be in one box like the AudioGD NFB-11 or your M-stage, with the preamp stage being capable of routing it outside of the box instead of its own amp output stage; separate with the DAC in one box while the preamp stage on the amplifier has that same bypass route, like on Schiit DACs and HPamps; or something like what Meier does, which is put a preamp output on the DAC and then have a headphone amp. The first one has something like the AudioGDs that have a selector switch out front for the output to be either headphone, DAC direct, or preamp output; the last one allows for using the speakers getting a signal to their amp off the DAC's preamp output without having to switch the headphone amp on or off (if it's on, just take the headphones off and lower the volume on the headphone amp).
So. Your over all statement is that an upgrade to the Darkvoice DV336se would improve the sound of the hd600s?
From a technical standpoint, the HD600 will get more power since OTL amps are designed to pour out more power into 300ohm loads than at 32ohms. And while looking solely at the distortion levels alone could mean you're getting more distortion off an OTL amp, if there is any audible distortion on the M-Stage when you crank it up driving a high impedance load, then you're just trading lower levels of what is usually sharper sounding distortion on solid state for higher levels of more pleasing distortion on the OTL. So on the HD600 it
might be a beneficial sidegrade. Wouldn't really call it an upgrade or downgrade.
Of course, there
are some other considerations. Tubes wear out sooner than solid state components, and AFAIK the stock tube set will set you back around $100. That said, at least when tubes conk out you don't have to whip out measuring equipment to figure out which chip is busted and then a soldering iron to take them off the board - you just pull these off and put new tubes in. Also, while tubes have a shorter life, it's not like all solid state components will absolute always last longer, and when one does conk out, they're harder to diagnose and replace.
Another is the power delivery profile. OTL amps are output transformerless, which means two things. Power delivery is biased for 300ohms vs 32ohms - not only in terms of output level but also that it has a very high output impedance. The HD600 has a high senstivity of 97dB/1mW, while the HE400i and AKG K&xx series have 35ohm and 62ohm impedance but a sensitivity of only 93dB/1mW. To put that in perspective, your M-Stage will pour more power into the HiFiMan and AKG,
but despite putting less power into the HD600, the max SPL that these headphones will reach will be within 2dB difference anyway since the HD600 is more efficient. it would have to drastically drop output at 300ohms for this to be a total disadvantage to the HD600. The OTL amp will basically pour more power into the HD600 that it doesn't necessarily need, while having an issue with the low impedance of the HiFiMan and AKG due to the lower output level at that impedance as well as the high output impedance on the OTL amp, which can either make the bass bloat or thin out.
Would there be any reason to keep the m stage? I'm starting to get into collecting different headphones for different musical experiences.
Perhaps the m stage will be worth keeping for other cans?
You can drive low impedance loads with it. Although personally since the M-Stage isn't necessarily that bad an amp for the HD600 you might as well save what you'd spend on the low cost OTL amp now and save up for a transformer coupled tube amp that has high output and low output impedance for low impedance loads but still have enough power into 300ohms like the M-Stage, and still have distortion ratios more comparable to a solid state amp, that way you wouldn't have too much tube distortion, but just enough to soften the tendency of solid state amps to have rougher edges. Look into the WooAudio WA22 for that.
The downside to transformer-coupled amps though is the cost. They tend to use more transformers as on the WA22 so they'll cost more, and that one also uses more tubes, so your routine maintenance will be higher (although again at least you can just pull the tubes off instead of soldering on chips). Alternately you can just get a hybrid amp like the Schiit Lyr2, or a better, smoother sounding solid state like a Meier Classic (and the DACcord to go with it) or a Violectric.
