Is there any way to double or increase line level preout voltage

I have Dayton spa500dsp plate amp. Saturation voltage is 2v
All receivers I have have pre out max voltage 1v

So the sub sounds underpowered. Low volume
Is there anyway to increase preout voltage

I looked at some line level boosters.. just want to know if there are any work arounds
In the receiver increase the feedback resistor value on the last gain stage. If op amp, from output to inverting input. If common emitter transistor, value of resistor from collector to base.
1 v output is stupid, another reason I use earphone jack of portable radios instead of receivers for my FM source. Earphone jack will go sometimes to 7 vac.
Warning to newbies: Voltage over 24 from one hand to the other can stop your heart. Use one hand at a time when measuring, use a clip lead on the negative probe. Wear no jewelry on hands or neck, 1 v can burn your flesh to charcoal through metal. Wear safety glasses soldering, especially unsoldering, solder splashes.
Solder tutorial on
I really appreciate the suggestion
Headphone jack definitely outputs more than pre out
Sub is perfect now with more room to boost bass at low volumes

Is there a way to measure output voltage with multimeter on headphones

It's nakamichi ta-4a. Don't think this voltage is anywhere in manual
Sounds like around 4v
You can cut up a dead headphone and strip the wires to get a measurement point. Else buy a headphone plug and put alligator clip leads on the shaft & tip contacts.
DVM other than the $170 Fluke RMS one produce random numbers on music. The AC scales are specific to 50-60 hz power line frequencies. Analog VOM with a 20 or 25 vAC scale is perfect. At the low impedance of a headphone or speaker output, a 5000ohm/v analog VOM from the hardware store will do. In circuit I use a Simpson 266XLPM from 1988, which is still for sale in non-shock resistant versions. No electrolytic caps to go bad in it, unlike a scope.