you are correct. line level is typical radio speaker level. I would double check that that particular sound card doesnt lock up on hibernate or standby though, I recall soundblaster threads about that.. not sure models... But if you want to know the cards low level output it would be in the vicinity of 0.3V-0.35V, not sure your amp type but check the model number in google to see what it's Nominal Voltage input range would be on preamps as if it's a lower grade amp the .3v would not be sufficient enough which can cause "whining" or buzzing noise in speakers. I have a Sony and it's min voltage range is .3V I simply turned up the gain to compensate the low voltage and it sounds loud, very loud! no noise..