I have both the TS premiums and Groneberg Quattros IC's. I can vouch that Klaus is definitely correct by saying that the Quattro's is about 80 to 90 percent of the TS Premiums but cost less.
Now, I replaced all the plugs from my Quattros with Eichmanns and I believe that they are about 95% or equal to the TS premiums. In the CD player to preamp chain, the TS premium I believe has a slight edge but on the preamp and amp chain, the Quattro is the winner. Maybe because the Odyssey monos are wired with the Quattro that MPT (max power transfer, thus matching) becomes so good.
On my TT set up (Lundahl step up to Wright phono to preamp) I don't discern any difference between the two on the mid range and highs. But the Quattro has a better bass to mid-bass weight than the TS premiums. Go figure!
BTW, I tried Bolder M-80( used, bought 2 pairs) because somebody posted here that it is better than the Gronebergs. In my system, the M80 is nowhere near the performance of the Gronebergs

. Just a thought....