Hi BeatleFred,
I don't think anyone can tell you WHY the Gronebergs sound the way they do, and from your asking what makes them "special", it sounds like you're being cynical due to some bias you seem to have about the construction...
Frankly, I don't honestly think anyone CARES about the wires being thin, or that they're going for the whopping sum of $150... what I believe others, including myself do care about is the sound they impart to ones system...
Personally, I had bought into the advertising and reviews on so many IC's it wasn't funny, and I spent a lot of money on wires which did not give me a full, balanced, transparent, satisfying sound with excellent high end extension, incredible imaging and 3 dimensionality, and a very deep bass where each note had weight to it until I tried a pair of Gronebergs... THAT is what makes them so special...
In my experience I have had somewhere over two dozen different makes and models of IC's in my system, and sure, I continued trying others even after I'd found the Gronebergs, but none has produced the realism the Gronebergs produce in the position between my pre and my mono's as the Gronebergs did, and none has produced the palpable sense of presence of the images appearing on my soundstage as the Gronebergs... the fact they can do this with two thin wires is most likely what helps in keeping the price low, but it certainly does not affect the quality or their ability to outperform other IC's going for many times their cost in the slightest.
If you're truly interested in the physics behind the design, I would suggest you do some searched on "skin effect" and look into some other info on "litz" wire. I came across some excellent white papers which explained why a thin wire is sonically superior in certain applications when I searched for information on the subject myself a few years ago, and you will find there's plenty of find plenty of documentation available from engineers, DIY sites, reviews on audioasylum and numerous other sources, which will explain that it does not require a large diameter wire to produce exceptional sound, and in fact a large wire guage in many cases produces an inferior result.
There are many factors which affect the sound you hear from a set of wires, including not only the conductors themselves, but also the insulation material, the brand of connector used, the solder, the number of twists in the wire and so on. In time you'll find it's best to let your ears be your judge, and not to be so concerned with the cost versus construction aspects. I have had IC's ranging from $80 up to $1,000 in my system, and those Gronebergs with those two little red wires have blown away the competition in every case, specifically in the position I previously mentioned in my system.
I recently auditioned some other IC's that numerous people have posted as being incredibly transparent, detailed and 3 dimensional... the Gronebergs were superior to them... why...? Frankly I don't care... they simply sound better... producing a presence and accuracy of Timbre unmatched by anything else in my system. After exchanging several emails, I had a conversation with the manufacturer of these other IC's a short time ago and explained to him directly what his wires were not giving me compared to the Gronebergs. He was thankful for the information I provided him with and understood I had given his IC's a fair evaluation comparing them for nearly two weeks on numerous source material ranging from symphonic, to fusion, to heavy progressive metal...
each of which the Gronebergs had not trouble handling at all, and provided clearly superior sonic performance with...
Will I keep searching...? of course... that's the nature of an audiophile... "you never know" and "what if?" are an audiophiles catchphrases... am I completely satisfied...? that's not possible with people who are obsessive as we as audiophiles are... do I think $150 is too much to spend for what you get...? If you're looking at sonic value, you've really got to be kidding... you are kidding, aren't you... What other IC's could you have possibly compared your Gronebergs to, and what in the world kind of equipment do you have if you're not kidding...
Perhaps you'd be happier in the DIY world, attempting to get world class sound from $20 - $50 in parts, and trying to convince yourself that what you've got is superior to anything else out there... if that's your mindset, you will find a lot of recipes for making cheaper wires available on audio asylum and other places on the web... but if you're interested in finding what sounds best in your system, regardless of what the cost factor is, use your ears and forget about construction techniques and why you paid so much for wires that are so thin... if you take apart every wire out there, you'll be dissatisfied with an incredible number of wires that don't meet your standards for value... if however, you use your ears alone and nevermind pulling every connector apart to see how it's made, you'll find you'll have to do a LOT of searching and spend a LOT more money in most cases to come close to the sound a well-broken-in pair of Gronebergs will impart to your soundstage...
