No I can't say "flat" at all. I'm hearing detail, openess, musicality, and as was described in a review, dynamics. Unfortunately I had to sell my P-51 to buy the Rx so I can't do an AB test. The P-51 is fantastic. I used it for a long time and a Hornet before it. If I had to list them as bassy and/or punchy I would go, Hornet, P-51, then Rx. In no way am I saying that the Rx lacks base. I believe it represents highs, mids, and lows equally and powerfully which creates the dynamics. I wanted the Rx, not just because of the good reviews, but for its form factor. I just got an iphone 3gs and wanted an amp that would lend to the phone's shape. I was worried about parting with the P-51, but am greatly relieved and excited with the Rx. It surpassed my expectations all the way around. If I had the money right now I would rebuy the P-51 or Shadow, and put in an order for the Pico Slim. It's getting great reviews as well.