Losing volume when sub is hooked up

wow herman, great research work. and i think you are 100% correct on this. i guess that is why even rel says to use the high level neutrik speakon cable and connect to speaker jacks on preamp. the manual says the impedance is 100k for high level inputs. did you see that? ok, i really wanted to make sure there is no problem with my preamp. i'm using the high level inputs. thanks again herman. makes me feel much better.

herman, these are specs on my integrated if you didn't see them already...THE M100SE-PLUS -- REMOTE VOLUME AND SELF -BIASING
EL34 integrate amplifier might be the most successful model in CONSONANCE tube products line. Including M100,M100MKII, M100SE and M100plus, the well improved push-pull set has already satisfied more than ten thousand user around the world. This amplifier may also be ordered in 300B version named M100Splus or 6L6GC version named M99plus with less power output.

Features:

1.Class AB,push-pull design delivering 40 watt output power.
2.A pair of EL34 output tubes running in ULTRA-LINEAR mode per channel.
3.12AT7 and 6SN7 dual triodes for input stage and drive stage (one 6SN7 drive pair of EL34).
4.Little negative feedback with precision RC circuitry for more linear output.
5.IEC Jack
6.REMOTE VOLUME CONTROL
7.SELF - BIASING

SPECIFICATION:

CONTROL FUNCTIONS: Volume, Input, Power On/Off
POWER OUTPUT: 40 watt x 2, RMS 1kHz
TOTAL HARMONIC DISTORTION: less than 1%(40watt, 1kHz)
FREQUENCY RESPONSE: (-3dB points at 10 watt) 6Hz-60kHz
INPUT SENSITIVITY: 180mV
INPUT IMPEDANCE: 100k
OUTPUT IMPEDANCE: 4,8 ohms. (User selectable.)
SIGNAL/NOISE: 90dB
CONSUMPTION: 90watt
INPUT INTERFACES: 3 groups (RCA) - 1,2 and 3
VACUUM TUBE: EL34 x 4, 12AT7 x 2, 6SN7 x 2
DIMENSIONS: 446(L) x 264(W) x 155(H) mm
WEIGHT: 17kg(net);17.5kg(shipping)\

Yes, 100K input on the speaker/high level inputs is a very easy load for your integrated. I agree that is the best way to configure the sub in your system.