I have the T3 and the D4 - T3 is good for IEMs but not much chop with fullsize cans. I'm sure that Skylabs final rankings wont agree with everyone, but he spent a crazy amount of time reviewing these amps - my suspicion is that anything from the first 3 tiers (and beyond) would keep most of us happy, and his list provides good background info on some very well-known amps:. Apologies for repeating such an extensive list, but I think the OP should consider all his options if he is willing to spend P-51 money. There is no *absolute* ranking, and I suspect that HeadphoneAddict rates the P-51 a little differently to Skylab, but its good to have access to the reviews behind these rankings. (I removed the reference to the Larocco amp which has been 'long ago discontinued' - doesnt make much sense for those looking to buy an amp in 2010).
http://www.head-fi.org/forum/thread/214588/review-portable-amp-roundup-56-portable-amps-reviewed-and-compared-last-update-12-20-10-added-rsa-sr-71b
Level 1:
Triad Audio Lisa III @ $600.00; Power supply is $350 additional/ Triad Audio L3 (newer version) Review
here
MST Fi.Quest, @ $450 (Review
here)
Meier Audio Stepdance @ $350 (Review
here)
Ray Samuels Audio SR-71B @ $600 (Review
here)
Ray Samuels Audio The Protector (in BALANCED mode only), @ $475 (Review
here)
Level 2:
Qables iQube @ $605.00
RSA Mustang P-51 (review
here) @ $375.00
Level 3:
ALO Audio RX Mk II @ $449 (review
here)
Headamp Pico @ $349.00
Meier Audio 2MOVE (and the older MOVE) (3MOVE @ $270.00)
iBasso Audio D4 Mamba @ $219 (Review
Here )
RSA SR71 @ $395.00 (original SR71, not the SR71A)
RSA The Predator @ $475.00
RSA The Hornet “M” @ $370.00
iBasso Toucan @ $229 (Review
here )
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I believe that Ray has made a concerted effort, along with other amp manufacturers, to bring the size of his portable amps down to something closer to 'pocket-sized', but for me that is low on my list of priorities. Common sense tells me that putting more power in a smaller enclosure must manifest itself in increased heat, but that is something you need to confirm when you have narrowed your shortlist to a single amp