Hello, I have bought mt-604 and chained it with A90 & D90 recently. This change does a significant improvement in sound so i barely can tell the difference between LCD-3F and 4. D90 works as DAC (not a preamp), a90 works as preamp on low gain, mt-604 has volume almost maxed out. A90 used for volume control so you dont need to touch mt-604 nipples. I am really impressed.
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