Tuning Rel G1

I just bought REL G1 Sub-woofer, which I connected with Krell S1500 Power Amp. I am using High Level Input with Synergistic Research Tungsten cable to connect. Speakers used are B&W 802D's. I went through REL manual 4 or 5 times, and followed the directions to set it right.
Problem is I tried crossover frequency from 32HZ to 40HZ, but I cannot have a volume opened more than 6 or 7. I spoke to several people and there recommended volume level is 14 or 15. If I set the volume level on sub-woofer to 14 or 15 my apartment shakes and base is extremely high.

Any advise?
Trcns First I'm not into HT. But I can answer your first 2 questions.
1) The Sub peaks out at 25hz but is not cut off completely. Like the speakers are not cut off at 34hz they are still going to 27hz but at a lower loudness. And the sub is still adding above 25hz again at a lower loudness. You want to find the crossover point where the 2 blend together.

That brings up phasing/timing. If the sub is 180 degrees out of phase with the mains you will get very deep bass but a huge suck out at the lowest the mains can do because the low frequency waves are cancelling each other. Don't rely on the sub phase adjustment to get them to be in sync. You may need to move the sub a bit closer or farther to achieve that. Again you don't want the bass from the sub either leading or lagging the bass from the mains. IMO that's the hardest adjustment.

2) Yes it will but minor. I didn't believe that until I got a demo with Dyn C4's and a Rel B1 playing a track of Diana Krall. Her voice sounded much richer and fuller with the sub. What was interesting it wasn't that way with all tracks. When I asked why it wasn't the same with all tracks he told me he couldn't explain it. But when he was trained by Rel to be a dealer they suggested that track to use as a selling point (BTW I don't remember the track or cd) .

Hope that helps
You might have also bought too much sub for your apartment.. I suspect a G2 or even a S5 might have been a better match..

Also if you bought the Rel from a dealer and spent all that $$$ maybe they'd come over to your place and help dial it in..

Also take time and read the Rel setup guide.. then read it again.. There's a lot of really good info on the correct way to setup the sub..

Did you at least get the phase correct? That's the very first thing to get setup correctly.
I dropped the Crossover from 35 to 25 and then even to 20 hz and started to increase it little by little. At 20 to 25 Hz I had to increase the volume from 6 to 9 but after 25 I had to go back to 6 otherwise the bass was too high. I also spoke to my dealer who sold me the subwoofer, his was same as I stated in my conclusion. Also last week I had Audio Professional to tune my system for room correction.
Conclusion: As everybody on the form said, volume number does not matter. Adjust it where it sounds right. Right now my sub is still set for volume number 6 and crossover of 40HZ. At 40 Hz sound stage does improve as compared to at 25Hz. There are some songs which have more bass than the others but overall the result is pretty good.