I have an Audio by Van Alstein Fet Valve 600R amp, unbalanced connectors only , 300 wpc. 20 to 20 kHz into 8 ohms, input impedance 500,000 ohms, with matching Fet Valve CF preamplifier with 20 dB line gain, dac is Topping D90. I have experimented with dac direct to amp. Desirable volume going...