I talked to the guys at Schiit regarding their, uh, "aloof" description of the Valhalla's strengths and weaknesses on the site. They specifically told me that while some people "like" the sound of the Valhalla with the Q701, (as I'm sure I would), that it really can't power them well, is not designed for them, won't get you a lot of volume, and isn't really the best choice. Again, they suggested the Lyr as the far better choice.
I don't think this is at all a "we want more money" situation, but simply a "we want you to be really satisfied with our stuff, so buy what is properly designed for them" situation. And having used a lot of underwhelming amps with the AKG in the past, I would certainly have to agree. It's worth doing the research and ponying up a few more dollars when possible to get what is designed and what will work well with your headphones. IMO of course.
To better answer your question, I think it'd help to hear in your own words what you like in the M-Stage, and what more you might be searching for. What I loved about the M-Stage was that it handled my K (not Q) effortlessly, and drove them well. It also sounded great, and fairly warm for a SS amp, again with my K702. I have not heard it with my Q yet. However, when comparing it to other amps, I could clearly hear a loss of detail, sustain, and sparkle with the M-Stage. It wasn't so much that it sounded bad; it didn't. But that I knew the AKG was capable of so much more than the M-Stage was able to provide. I'd assume it'd be the same situation with the Q701 as well. That's just an assumption, based on the same driver being in both cans, and others can chime in (or chide me) on that.
The Matrix was my tide-me-over amp anyway, while I saved the money for a Glow. And that is the amp I am extremely happy with, and I've stuck with, after many trials including the Grace 901, O2, some quality vintage gear, several low-end Headroom amps, two Wheatfields (both of which I loved), and many other portables. I'm sure there are a ton of great amps I missed, but I love the Glow and about the only other amp I'd love to try would be the Woo 6. I'm into the idea of the Lyr, but everyone has said it's painfully easy to blow your cans and your eardrums with those, so I've passed. I suffered an ear injury a few years ago, and don't want to repeat that experience ever. Plus, according to several threads on this site, the Garage Amber sounds comparable (dare I use that word anymore in this thread?) at a much lower price.
Check out the Garage Amber. I was all set to buy a Lyr immediately, but after a lot of reading I figured the Amber would be worth a try, and it works well with the Q701 and has great customer service, just like Schiit's stuff. But it's a $130 cheaper. I have not heard either; but if you're struggling with cash, it may be worth a try. I personally decided on the Amber, but then got a lucky break and was able to get a Glow again. I'm currently in a holding pattern waiting for both my Glow (newest model) and Q to arrive. I live overseas and buy from the US, so it's always an issue getting heavier stuff sent to me. I may have to just go pick it up in person when I visit.
On burn-in, I've only experienced a whopping difference between out-of-box and 100 hours (or so) after use with two headphones: the M50 and the K701/2. I've heard a lot of people with the Q701 have experienced the same, and of course one person reminded me that he thought they sounded great out of the box. But, you're not alone if you've experienced a little harshness or other unhappy sounds "just out of the box."
Edited by Kouzelna - 10/16/13 at 2:28am