software

Hi, I'm a newbie jumped into this forum

I grabbed Schecter A-7 Diamond Lefty with Duncan Designed humbuckers recently from ebay. This is my first 7-string so I'm so excited and played after I got it. I used Korg Ampworks thru the monitor speaker for testing. Then I found something strange.
Right now I tuned the 7th string as B 1st to 6th strings are normal tuning.
When I played E power chord, means E open 6th and B on 5th string, it sounds as E chord since E is the note stands out. But when I play the B power chord, 7th open string and F# on 6th string(2nd fret) , it doesn't sounds like B chord. Actually, F# note stands out more than B, so it sounds a little weired, something like F# 4th chord. I checked the tuning but the tuning was fine. The loudness level of 7th string is not so little when it is played alone.
Would it be the problem of Duncan Designed's limits? Or would it be the Korg Ampworks? I don't think it's problem of the monitor speaker since I also play the bass frequently thru it, so it can handle the lows pretty well.
Please let me know anybody has an idea. If it's because of the pickup, I may replace it with genuine Duncan.