Dear @mulveling : " I think it’s a side effect of suboptimal setup or system balance. We don’t deserve to torture ourselves just because a new component "should" be better! "
Other than cartridge/tonearm rigth set up the system balance it coverts in something as synergy that as mijos said is only that one link is covering/hiden other system link " errors ".
My take by first hand experiences tells me that if I introduce a true better new system link in the system we have we should be perfectly aware on it. This " perfectly aware " could be have its precense in different ways: could be that the system quality level performance was improved through what we listen in our sessions but could happens too that some or several of our LPs suddenly started to sound not very good because the new system link can shows us that those LPs that we though were very good recordings are not really good recordings for different reasons ( recording mistakes, not good recording mastering and the like ) but at the same time the LPs that sounded very good now sound excellent.
Yes, the new link altered the system balance and now " unfortunatelly " we are aware aof those LPs not very good ( as in the past ) kind of sound. In the other side a true better system link can shows hiden system " errors " and this new link function as a tool to make a system check-up..
Like it or not ( your " torture " ) a new true better system link that we just changed is for us a system " discovery "/recordings in many ways.
Each one of us try to have a system balance that goes with our MUSIC/sound priorities. Try to look for a live MUSIC performance could be a really good target even by you that are " oriented "/accustom to what you like. Today after all those 5 years with Koetsu you are looking to change that " but like all Koetsus it leans very heavily to warm and full-bodied side of the spectrum "..
I owned several Koetsu cartridges and the first one that really made " honor " to MUSIC reproduction was when appeared the Platinum one and my KRSP performs way different to the other pre-Platinum cartridges where that " heavely to warm " goes way lower but as my system gone and goes improving that " warm " just almost disappeared and I have a long listening session at my place with the Blue Lace.
Comparing your experiences with my experiences tells me that not necessary that that " warm " came mainly by the Koetsu but inside and around your system.
Now, I love the Colibri and when runs good runs in an exceptional way and yes a little better than Koetsu and with excellent midrange. Remember that the midrange mainly depends of how good the system handled the bass range, it's here where we can or not have an excellent mid-range. Now, Koetsu and the Colibri are different performers and no till today does not exist the perfect cartridge in an universal sense because the objectivity need it for always losted against each one of us taste/subjectivity. That's why I said that could be a good target that our room/system have an approach of the live MUSIC balance and cartridges by it self just can't do it. Maybe some of us have to change ( we normally just don't want it . Nothing wrong with that. ) our MUSIC " approach " and if we don't do it will be really dificult to live in totally satisfaction with our room/system enjoying it as never before.
Yes, it is really hard to make a " radical " changes about but we have to try if we feel we need it to improve our MUSIC reproduction enjoyment.
R.