i got the set of HD-650 with 6ft Cryo Vampire cable 4-way, no Y splits, and tried them on the Heed.
The setup:
PC (Foobar 2000)>Focusrite Saffire(24/96)>Beresford Caiman (still burning-in)>Heed Canamp>HD-650
My opinions:
1. I thought the K701 detail was massive. I could never hear any hiss on the Stockfisch recordings. I listen to Allan Taylor and Chris Jones in lossless format to test my headphones. I can hear the hiss with the Senns, which means they are more detailed than the K701, i suppose. Not sure about this though.
2. I found out some acoustical recordings sound almost the same on the Senns compared to the K701.
3. Songs like Fleetwood Mac - The Chain will be handled from now on only with the Sextett MP, K-340, or the K-701, Nothing gets near them. I believe the drums sound on the refrain cannot be reproduced any better on ANY of the other headphone brands i've owned or tried so far.
4. Bass on the HD-650 was reproduced pretty nicely and i realised that i can push enough power on them through the Canamp and they don't seem to have them drivers blown. The same happens on the K-340 but there is no more power on the Canamp for them. I tested them with songs No Man - Counting, and Centrozoon - Little Boy Smile, which have massive bass. I think my stock green driver K-340 is the best here. Will handle bass like you cannot imagine. Other phones would have them drivers cracked at that volume. The Heed goes almost full blast and the K-340 volume is still bearable even that high.
5. I also tried the Caiman headphone amp output that seems to drive the HD-650 pretty good. They seem to be on the bright side with that equipment. It feels like as there is more treble to the general sound than the Heed but on songs where they perform the same it seems that the Heed has a LOT more punch. It is more powerful. I think it feeds more electricity to the phones even at the same volume level. The Heed though is a bit darker.
6. On some of the before mentioned Stockfisch recordings and more specifically Chris Jones - Long After You're Gone, there are places in the recording that both the Heed and the Caiman cannot seem to handle the guitar strumming. It seems that my cars audio system handles that pretty alright therefore i will retest tonight because i might be having the volume too loud or my ears are completely damaged.
Will get some other opinions out as soon as i get home.
Just so that everyone knows what I've tested so far with the Canamp:
K-340
K-500
K-340 (KT-88)
K-240 Sextett MP
K-701
HD-650
They all seem ok however the HD-650 is still pending some testing. Overall, it is the only phone that i've noticed that it sound VERY good on some recordings but VERY bad on others. Maybe because of everyone's comments over here, that it is not a good match for the Heed, i was expecting too much or a few reasons to buy me a new amp.