I have the Caffeine Pro, Lyrix Pro, and Lyrix Pro Total.
The Caffeine Pro was the basis or "starting point" for the design of the Lyrix Pro, and the actual circuit topology is very similar (similar does not mean identical). The sound is also very similar once fully burned in, with very small (5%) increases in performance each time you move up the product line. My Caffeine Pro is very difficult to tell the difference in sound from my Meier HeadSix. The Lyrix Pro Total is easier to hear the difference, with a slightly bigger soundstage/headstage and transparency.
If a person thinks any of these amps above are too bright, I am fairly certain they wont like the Headamp Pico, iBasso D2, iBasso P2, iBasso D1, Meier HeadFive and HeadSix and 2MOVE, or RSA Tomahawk either. The Predator is only very slightly darker in tonality, but it's sound carries a lot of weight, like an amp 10x it's size.
Here are a couple of old reviews I did ages ago:REVIEW: PenguinAmp Caffeine portable headphone amp w/BASS BOOST - Aka HEADSTAGE LYRIXREVIEW: Headstage USB DAC Also Reviewed Meier HEADSIX, iBasso D1 and Headstage Lyrix
Deep link to the amp section review: http://www.head-fi.org/forums/f46/re...ml#post3398212
And a newer one:http://www.head-fi.org/forums/f5/min...-micro-306883/