Just got Audible Illusions L1, but it sound harsh


I just got a Audible Illusions L1 preamp to replace my Rotel RC 1070. I can hear it is much more detail, it sounds more forward and bigger sound stage. But I also found it too harsh. Especially in vocal, the "s" sound is very loud and quite alloying. I don't have it in my RC 1070, but at the same time, it doesn't sound as musical. It is just like sing behind a curtain. I don't hear that detail, but also, those annoying "s" sound is "filter" out. Is it a characteristic of this preamp? Is there any thing I can do? I am using a Rotel RB 1080 amp. Should I try another preamp? Or try another amp?
gte357s
The pre-amp has been running for an hour. I am not sure if I use the right term. Maybe that's what people called CD glare? I am listening to a female singer pop song, where it is medium to high treble. I tried using the CD input of the L1 where there is a circuit to remove CD glare, and it is a bit improved. And I also tried connecting the L1 to Rotel through a RCA-XLR cable. In Rotel, the balance input gone through an opt-amp, and the glare is removed, but then it sounds very Rotel, sounds very similar using the Rotel 1070 preamp. It seems I either have this glare, or some less musical, "filter-out" sound.
i think before you drive yourself crazy to take it step by step

in my opinion the first best step would be to replace the tubes. try something older and US made first . Ebay would be a decent, cheaper source
The pre-amp has been running for an hour
Gte357s (Threads | Answers)

1 hour is not enough time to start doing critical listening. Your preamp and cables need more time than that to settle in before you make judgements. Give it at least a couple days then if still necessary start thinking about tweaking things.
The piece of gear in question is about 10 years ago, how much more is it going to settle in?
Face, any component and the associated cables need time to settle in. 1 hour? Not enough imo. Is 1 hour adequate for you to start making assumptions about performance? At minimum I wouldn't conclude anything for at least 24 hrs after putting new (used) gear in my rig.