[JanaSA]

Hi,
 
Firstly what a wonderful and informative community this is, I'm new to the world of audio and have really benefited from the great wealth of knowledge and experience that is shared on this forum.
 
I've recently purchased the Beyerdynamic DT 770 Pro (80 OHM) and I really enjoyed them coming from standard headphones, but after purchasing the Yamaha EPH-100 for on the go I couldn't help feeling I wasn't getting the best out of the DT 770 Pros, both in terms of volume and sound presence.  I am using the Fiio E7 as a external DAC/Amp connected to my laptop, and listening to the EPH-100 the DT 770 Pro both sounded significantly lower in volume and less dynamic.  I am guessing this is something to do with the impedance, the EPH-100 is 16 OHM and the DT 770 Pro is 80 OHM.
 
Firstly, could someone shed light on why the EPH-100 sounds better than the DT 770 Pro?  I hope it's because the E7 cannot do the DT 770 Pro justice.  If this is the case then I was looking at alternative DAC/Amp combos, and the RSA Predator looked quite good:
 
http://www.raysamuelsaudio.com/products/predator
 
Is this a worthwhile purchase, will it deliver significant performance and better drive the DT 770 Pro?  I really want to avoid spending $475 if the gains are not at least some what in proportion with the cost!  How much of jump would it be over the E7?  Or should I be looking at other DAC/Amp combos that might be better in performance/suitability/cost?
 
http://europe.beyerdynamic.com/shop/hah/headphones-and-headsets/studio-and-stage/studio-headphones/dt-770-pro.html
http://uk.yamaha.com/en/products/audio-visual/headphones/eph-100_silver_w/?mode=model
http://www.fiio.com.cn/product/index.aspx?ID=28&MenuID=020301
 
Thanks,
 
Jana