To convert the voltage from 100V to 120V, Move K3 to K5 and K4 to K6 position.
Voltage conversion on E-600, E-650 and E-800 basically similar, first row of connections for 100V, second row for 120V and third row for 220/240V.
For 100V and 120V mains, soft start resistors jumpers and fuse value remain the same.
For 220/240V mains,disconnect jumper J1 and J3, install jumper wire on J2, change fuse accordingly.
Accuphase design those built in power transformer for worldwide voltage, I don't think voltage conversion will affect sound quality.
I hope I've answered your questions.