Yeah since you're using the 650, I'd also go with the NX4. The only advantage the Q1 has is the even channel matching, but the NX4 has much more power. I can listen to most music at moderate levels on the Q1 with the 650 (single ended), but it only just barley gets loud enough. Definitely not loud enough for classical or quieter songs. NX4 pushes 59 milliwatts into the 300 ohm Sennheisers, the Q1 outputs only 7.4 milliwatts (or around twice that much using a balanced cable).