Thank you, now I get it!
Why do I liked D600 with Crack -- it has much less prominent bass, healing overall balance.
But T1 with Crack is just awesome. The sound is stunning, I could not stop listening. May be it is due to my first experience with tube amps (Shiit Magni, Audinst mx2, Fiio e17 my previous)?
Highs and mids are so beautiful, clear and liquid like. On the other side, while bass is pretty good, but not at the level of mids and highs. I am wondering would it be healed by Speedball Upgrade?
The speedball does exactly what it say on Bottleheads product page
"The most immediate thing you will notice is a better sense of clarity. Things get tighter and quicker, bass and midrange get cleaner and more dynamic sounding, and the background gets more quiet. As with all of our upgrade kits, the improvement is easily heard"
You might want to take a little look later on at the Cracks upgrade path. The T1's just scale amazingly well with a few selective easy to do mods. There are a few T1 users running modified Crack combos here.