ReL Subs: High Level or Low Level connection

I just compared using Hi level vs low level

At a given amp level and the same music the high level is 1-2 db higher than when using low level using my Pass Labs INT-60

High level sounds a bit better to my ears.

I'm a little disappointed as I was hoping to sell these baseline blues 

For all of you who uses the high level connection. With the sub on and volume all the way down, does your main speaker sound different than when the sub is completely off? I have a feeling high level connection is effecting my amp somehow, like what Mijostyn said earlier in the post.

I forgot to mention I’m using S510 driven by Luxman m900u with Magico Q3 as main. When the sub is on and volume down to 0, the Q3 sounds less transparent, warmer with more midrange body. So I’m wondering if the high level connection is effecting the Luxman.