Wow, all this talk of the GS1000i has me salivating...
I have tried the PS500 (three different pairs) and every time the bass felt too warm, too thick, too obtrusive. If I felt this way, would I feel the same way about the PS1000? I've always wanted to hear the PS1000.
I've never seriously considered the GS1000i because everything I've read about it seems to suggest it's too bright to listen to at moderate volumes and that the mids are too recessed. So are these non-issues with the "i" models?
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Concerning the Magnum route, I can share my experience with that. I have a Woodied Magnum V4 setup, and the first thing I noticed when comparing it to Grados is that it really does sound like Grado. So if you're worried about a substantial departure from the Grado house sound, then I wouldn't worry. Magnum V4 in Grado ear-cups sound like a Grado headphone.
Where the differences lie is the mids, most notably. The Magnum V4 mids are the best mids I've heard from any headphone. They take the magic that Grado has in the mids, and they find a way to make it slightly more refined. This means they still sound forward, but not with the fatiguing forwardness that I personally find Grado mids can have. Not only this, they lose the "shoutiness" sometimes present in Grado models, which makes for a smooth ride and, like I said, the best mid-presentation I've heard.
As for the bass, it sounds to me very neutral. It's still Grado-like, but it doesn't have as much kick or impact as the RS1i's I've heard. This could be the particular V4 drivers I have, or the driver-earcup synergy, but whatever it is, it sounds actually quite neutral to me, non-fatiguing and unobtrusive. Still, I wish the bass was more RS1i-like.
The highs seem great too. Very natural, life-like sounding highs. Smooth in that the highs do not sound peaky, which Grado highs can sound at times.
The only deal-breaking issue I have with the Magnum V4's is the sibilance. My pair, for whatever reason, seems to have trouble dealing with sibilance. On really good recordings, this is a non-issue and the headphones sound terrific. But on most of my music, the V4 displays a sharp sibilance that my SR60i does not.
That said, I have the newest update of the Magnum driver being shipped to me as soon as Jin at TurbulentLabs gets the shipment from Rhydon. I'm hoping that it's just my particular V4's that are sibilant, and that the V5 doesn't have this issue. Supposedly, the V5 has better bass extension and slightly more impact, so if it doesn't display sibilance and indeed improves upon the bass of the V4 without reaching PS500-like obtrusiveness, then I'll have exactly the Grado-like presentation I've been longing for. I await.