should I stay with Audio Research LS25 ?

Yes, get rid of your preamp as soon as possible. It's awful. Sell it to me :)

Why are you thinking of trading? Is there something in particular you don't like about the sound in your system?

To answer your question, NO !
Make sure you have a good power cord for the ARC and good tubes and enjoy it.

An ARC LS26 is being rumoured to be replacing the LS25 Mk. II shortly.
It is apparently a scaled down ARC Ref 3. If precedence applies, it will have the same price tag as the current LS25. And if its sound is related to the Ref 3. . . it will likely prove to be quite delicious!