Which Phono Pre?

Can't do chakster, have not heard either one. Back in 1980 a friend did have a Threshold preamp that had a phono stage, a super wide band unit. It was difficult keeping it quiet (hiss) but it had an excellent phono stage for the day. I can not remember the model number. I never could remember names and numbers. Back then all preamps had phono stages. The idea of separate ones had just gotten to the market. Again, thank you Mark Levinson, the man who proved some people would spend ridiculous money on HiFi gear. The first stand alone phono stage was battery powered and I do think it was designed by John Curl. It cost something like $1200.00 which was steep for the day. Found it!   https://www.google.com/search?q=Mark+levinson+JC1&tbm=isch&ved=2ahUKEwimlc-7qfvwAhUocjABHSnZ...

Raul is absolutely right. The Pass Labs is special and beautifully made. It will last a lifetime. The 4 Point is one of the best arms for a Koetsu. With the 11" 4 point you might have to add a little weight to the head shell as the Rosewood bodied Koetsus are lighter than the stone bodied units.
Soundsmith sells a great set of graded cartridge screws. With a Hi Fi News Analog Test disc you can get the resonance frequency right down to 8-10 Hz and your bass will be wonderful. The only other thing I can think of that would make an additional sonic improvement would be a low profile MinusK platform under the Firebird. After that I don't think you could do any better regardless of the money you spend. You are right at the point of rapidly diminishing returns.