I have the Jeff Rowland Model 625 ( not S2 like you).
I have notice more bass with Isotek Synchro.
I have Furutech Flux 50 NCF with Jeff Rowland Corus, Esoteric K-03XS, Grimm CC1, Accuphase C47, and before Flux 50 NCF, I have Isotek Nova GII.
I have pass an order for 3 NCF Booster and 6 others NCF Booster Signal.
I hope have them in the end of the January month.
I hope I notice big improvement.
Now, I have them one week ago.
3 per speaker cable, 1 for the preamplifier, 1 for the amplifier and 1 for the home theater preamplifier.
first test :
1 per speaker cable : sound was improved, more accuracy...
second test :
2 per speaker cable : second NCF Booster signal is in the middle of the speaker cable
No change ????
So second NCF Booster signal is just under loudspeaker connectors : sound was improved too..a little more 3D
third test :
1 NCF Booster on the preamplifier : big improvement, sound are clearer and warmer, a little more bass
2 NCF Booster signal per speaker cable
4th test :
1 NCF Booster on the preamplifier
2 NCF Booster signal per speaker cable
+ 1 NCF Booster on the amplifier : vocals are better in place, I can say that with Gospel CD...
The backing vocals are well behind the lead singer and the lead singer is well in the center of the two speakers, which was not the case before.
+ 2 NCF Booster signal per speaker cable just under the amplifie connector
5th test :
3 per speaker cable, 1 for the preamplifier, 1 for the amplifier and 1 for the home theater preamplifier.
For the Hifi, differences are present, we can listen some improvements in all domain, voices seem more naturel, but the big big difference is with the home theater.
On the 4K Bohemian Rhapsody, at the final of the movie, clearly, my friend and me are very surprised. It's not a litte improvement, but a big improvement ! Queen is in the room, voice are very very naturel.
Feels like at the concert, a feeling that I hadn't had before.
Do you believe I am crazy ?
Test them...You don't believe you will listen with this little accessories...
Hope this help !