Upgrade from Creative Sound BlasterX G6 for DT 1990?

Hi people! I have been living my happy life with Creative Sound BlasterX G6 as DAC/AMP and Sennheiser HD 650 headphones. Recently I've decided to try something else, so I've bought Beyerdynamic DT 1990 PRO MKII 30 Ohms.

I am pleased with experience, enjoying this bright and brittle sound. This success moves my hand to the wallet and asks: maybe it's time to upgrade DAC/AMP? Sanity check is not applicable, because G6 has enough power for these headphones. But more power will open new horizons for me. I seek for neutral sound, big serious box on my desk with big and convinient knob (G6's knob is not), buttons and balanced output (maybe for HD 650 experiments). I wish for options to connect CD transports and players (Line IN, Optical IN), because I have them and CD collection. Don't care about MIC IN and wireless.

I look at FiiO K7 BT, Topping DX3Pro+, but don't really know where I should stop price-wise, ready to spend up to $500, if it will be "Buy It for Life" (G6 is nice, but state of firmware and drivers is not healthy). So, should I, and if yes, what are my options?