Haven't heard the 650s; don't know anyone around here that has them, unfortunately. Glad the power handling on the Atticus would be good with the BasX juice; and as for the sound being different on each amp, I won't know the difference as it'll be the only amp I pair it with
I have an old Objective2 amp here as well, but I don't think it'd be enough to drive 300ohm drivers.
I don't have a massive headphone selection. I started with everyone's starter set, the ATH-m50s (still have them - using for PS4 gaming). Bought a set of Mad Dogs, used daily for 5 years. Upgraded them last year to Alpha Primes through Dan. I suppose I'm simply looking for a bit more punch / fun, as the low end on the Primes is good but not amazing. It seems like the Primes are finicky when it comes to music selection, source / amplification / bitrate all equal. On some rock / metal tracks, the bass becomes pretty muddy at high volume and the whole thing turns into a gigantic mess, but when it comes to any sort of EDM / Electronica / Trance, *wow* - clear, concise, LOUD. Color me confused.
I've demo'd a set of Denon D7000s which were very bright and I enjoyed them, but I don't think I could listen to them for 5+ hours a day without major fatigue. I plan to demo the Klipsch HP-3s based on Zeos' reaction - and there is a shop in town that has them.
At any rate, I'm only keeping one mid/high-end set and they'll be used at the office. Must be closed-back or mostly-closed back. A tiny bit of bleed is ok.
Edit: Looks like you've had the Alpha Prime at some point - you should get where I'm coming from!
ok the mad dogs/alpha primes are a good reference since those were daily listens for me for years, so i'm quite familiar with them. i'll focus on the prime in comparisons since it's the better performer. first, the muddy at high volume comment makes me think there was a power issue. i ran my primes from a lyr 2 and i could take the volume up to unbearable levels without distortion. i don't have a lot of experience with the a100 so i'm only assuming here. i had similar experiences running my prime on a fulla 2, once i turned up the volume it was insufficiently powered, and sounded quite bad.
as for sonic comparisons when everything is at full potential, i'd say the atticus is better, but not substantially. bass slam and impact is better on the atticus, but the primes hit fairly hard as well, so the increase might not be huge. some might think it's substantial, some might say it's marginal, it's very subjective. i'd say it's noticeable, but not night and day different. where the main difference lies, imo, is in quality. the prime is fairly precise down low, but the atticus is actually more resolving and textured. it transmits minute bass cues better. decay and resonance is more natural. the prime's decay is fast, so perceived impact is less. will that be enough to satisfy? that's the tough and highly personal/subjective question. for me, absolutely. for others, maybe not so much.
up from the bass, mids are more forward on the atticus. they sound closer, more full. fine detail again is superior on the atticus. male vocals have a weight to them that the primes just cannot match. mids are also warmer sounding. leading note edges are slightly more rounded, without the snap and bite the prime sometimes exhibits. it's hard to explain, but quite noticeable. the prime sometimes is a touch sharp and aggressive, something the atticus will not do.
highs are probably the biggest area of difference. the highs on the prime are imo a touch sibilant. they have a harsh metallic glare i found fatiguing at higher volumes. the atticus' treble is smoother, with less glare or harshness. on the flipside, though smoother and seemingly rolled off, the atticus actually transmits more treble detail compared to the prime. it's just slightly farther back on the stage, so you have to concentrate a bit more on it. but once you focus in, you'll hear micro details that the prime doesnt transmit as cleanly.
tonality is different as well. the atticus is warm warm warm. the prime is not as warm, it's more neutral or cooler sounding. notes dont the same weight and resonance as the atticus.
so i personally think the atticus is a worthwhile upgrade. but imo the gap between them isnt huge, and personal preferences will outweigh any technical differences.
i'll end with this, i'm a hardcore atticus addict, i cant get enough, so obviously i'm beyond biased. the atticus fits my preferences like nothing else has yet. finding what fits yours is key, and isnt necessarily the better set. i personally hate the utopia and think the atticus is miles better, because i just like it's signature better, technical abilities be damned.
i listen at work as well, and if i wasnt using an atticus, i'd be using the beyerdynamic dt 1770. the atticus took over the 1770's spot in my work lineup, but until it showed up, i was quite in love with it. i liked it more than the alpha prime, the t5p.2, and the ether c.
oh, afterthought on the atticus, it's far pickier with amps than the prime is, be warned. the dt 1770 is not amp picky, nor the t5p.2 or ether c, in comparison.