preamp for rowland 8TiHC

Tongpoh, the term 'better' is of course very relative. As far as I know -- per Jeff Rowland's own descriptions -- the Coherence series is lush, slightly warm in the mid bass, and very captivating. . . but just a little euphonic. JRDG's designs have evolved significantly since the '80s and '90s. You are likely to find the Capri to be more extended and linear, probably with a little more harmonic complexity, without giving up any of the traditional JRDG 'magic'. . . of course, Coherence will look more impressive, larger, heavier, much busier inside.
Ultimately there are no rights nor wrongs. . . It really all depends on what kind of sound is more desirable to you.

but i heard someone said the best JRDG preamp was Coherence, are you sure Capri is better than Coherence?

Tongpoh, have you considered getting a current production JRDG Capri instead? I have replaced my ARC Ref 3 with the Capri, and according to JRDG the Capri is more extended and linear than all previous Rowland amps, while maintaining the JRDG hallmark musicality. Don't let the tiny size, low birth weight, low parts count, and modest price of the Capri fool you. . . this one is a serious music maker. G.