How do I reduce the overall gain in my preamp ?

This is tedious unless you really know what you are doing. I would not attempt if you are not familiar with electronics. The circuit is "tuned" for all the parameters involved - you change one, you change everything. Just turn down the volume or get a different preamp IMO.

I put a passive line stage in my tape loop - for casual listening i have remote control also. works fine. When i'm feeling picky about sound i simply flip the switch turning off the tape loop. If you can accept some minimal signal loss (there will always be some) you can put a passive preamp of high quality between your amp and preamp but you must deal with the cable between the passive and the amp carefully to minimize the loss. I've done this with some success - not as funky as it sounds, but you'll get booted out of the audiophile corp if you tell anyone you did it!

I owned an ARC LS-1 and also had to tame this monster!
Call Lenard (at the ARC factory) and tell him your problem.
He sent me a diagram of the solder traces (bottom of circuit board) and told me where to sever a trace to reduce overall gain (it worked, of course).

I would not try to modify your preamp.

I would look at getting a different preamp or look at getting a source that outputs less. Or look at getting speakers that are less sensative.

Just my 2c.

KF

KF, I believe you meant poweramp and not speakers.

If poweramp is sencitive and source component(s) with high output why not going for passive preamp and sell the line-stage?