SCA J99, need guide to mod line input

Hi all, I'm new here, and have a very limited knowledge about electronic, so hope my post is not annoying or disturbing for You all.

I just considering a SCA J99 preamp after try one that I borrow from my friend, I really like it, but there are something that I think can improved, since this is designed for mic and my usage is in line level. Here are the schematic link from SCA:

http://www.seventhcircleaudio.com/J99/J99R36/docs/j99_sch.pdf

1. The input gain, the stock is too high, I think with 1dB per switch click is perfect for me, but how to determine the calculation of the resistors?

2. Is that the d1-d4 is a clipper? I found that if my input is high, I hear a clip/saturate sound that I suspect from this diode circuit, is it save to remove / bypass the diode to get more headroom and clean sound?

3. The input transformer is Lundahl LL1538XL that after I check is for mic input high gain, I think it will be better to use line input transformer to improve the headroom? What I must consider and take care of if I change the input transformer, circuit wise and transformer spec wise?

Thank You before, I need to know the possibility before decide to buy and build the kit, so any help, information, will be very appreciated.

Cheers,
Gabriel

The easiest way to make a line input out of a micpre is to put a pad in front of it.

Shure makes an inline pad good to 25db, but you may find you'll need more depending on the source.

Regards,
Mark

I would suggest using a line input stage rather than a mic pre.  There are lots of good and simple circuits available, even some on the Jensen website.  You are suggesting buying a commercial mic pre kit and then changing out much of what makes it a mic pre but it will be far from an optimized line stage.