Well, Syzygy, after 4.Bb5 Nd4 5.0-0 c6 6.Bd3 Nxf3+ 7.Qxf3 g6!? the circumstances have changed as Black has played (too) many pawn moves. Here White indeed plays 8.Bc4! d6 9.d3 Bg7 and now 10.h3 or 10.a4 (2 pages of analysis). Black cannot risk 8...b5?! 9.Bb3 a5? 10.d4! +/-

I don’t want to give much more details here, maybe I‘ll answer one or two general questions to other systems. 
While the overall claim of a clear += may be optimistic, it‘s certainly a good and interesting book with good strategical explanations and many little improvements. Btw, I‘m not defending the case of K/S and I‘m interested from the black side at least as much as from the white side.

tracke 

Hello Tauromachie,

as K/S put it, 6.Bd3!? does not seem so natural (...) but playing in this way White avoids the trade of his Bishop and does not allow his opponent to advance with Tempo d7-d5, or b7-b5. It‘s just the „minimalistic“ approach, K/S DO NOT strive for a direct clash (...) after the first few moves. 
After 6.Bd3!? should definitely exchange on f3, White takes back with the queen and intends Be2, d3, Qg3 and f4 in most cases when the Be2 prevents ...Nh5/g4. 
K/S do not mention Gustafsson‘s 7...Bd6!? . Generally it seems a little bit risky for Black to put the dark-squared bishop to the queenside when White attacks on the dark squares of the kingside. But maybe it works concretely, I‘m not the man to refute Gustafsson‘s suggestion. Looking at something like 7.Qxf3 Bd6 8.Be2 Bc7 9.d3 d5 10.Qg3 0-0  I prefer White while it‘s certainly very close to equal.
Since yesterday I checked several „= to += positions“ from this book with SF10, and there’s a strong tendency that in these almost equal positions the engine likes White‘s position the more the deeper it looks: not much, but often raising from eg +0,08 to 0,23 after some time ...

tracke 🙂

I got my copy this morning from Niggemann. Looks „practical“ and good!

I have to confess that I‘m no expert in these lines, neither from the white nor from the black side. So in the last hours I‘ve just cross-checked the book‘s lines superfically against some other resources ...
In the preface Khalifman characterizes his approach in this book as scientifically minimalistic: practical and riskless but always „on the bright side of the equality“. In fact the authors claim an overall += but of course in many positions it‘s not easy to decide if White‘s advantage is small, very small, microscopic or non-existent ...

Probably you want some lines, a few at least?!
A) Rubinstein: 4.Bb5 Nd4 5.0-0 c6!? 6.Bd3!? and after 6...Nxf3+ 7.Qxf3 d6 8.Be2 Be7 9.d3 0-0 10.Qg3 there are 4 pages of analysis, obviously improving on some recent games of Andreikin.
B) Symmetrical mainline: 4.Bb5 Bb4 5.0-0 0-0 6.Lxc6!? dxc6 7.d3 (from now on White‘s play is simple and harmless but straight forward!)
B1) 7...Bxc3 8.bxc3 Bg4 9.h3 Bxf3 10.Qxf3 Qd6 (as recommended by Ntirlis2016 and Johnson2018) and now after both 11.Qe2 (Nimzowitsch-Vajda 1926) and 11.Qe3 (Kasperian-Korchnoi 1952) the book offers an improvement.
B2) 7...Nd7 8.Ne2 (also 8.Bg5!?) Re8 9.Ng3 Nf8 and now 10.d4!? or 10.Be3 (along Firouzja-Yi 2016).
B3) 7...Bg4 8.h3 Bh5! 9.Kh2!? (with the idea 10.g4) is critical but += according to the authors

If you play the Spanish4Knights with White or Black you probably do not come around buying this book!?

tracke 

I think you have to wait.

Quote:

On 2 Nc3, 2...Bc5 is a serious extra option. 

The book is out on forward chess. He gives an early Bxc6 against the Symmetrical Variation, 5 0-0 against 4...Nd4 as mentioned in the table of contents, and what I understand to be fairly standard lines against 4...Bd6 and 4...Bc5.

ErictheRed wrote on 12/19/19 at 16:11:36:

Only if you dislike the Latvian and/or the Elephant.
1.e4 e5 2.Nc3 Nf6 3.Nf3 Bb4 as already mentioned is the Petrov.
1.e4 e5 2.Nc3 Nf6 3.Nf3 d6 is the Philidor.

I'm curious whether 2.Nc3 would be a better move order if one really wants to play the Spanish Four Knights: Black nearly always responds with 2...Nf6.  I guess it depends on how you feel about Black's second and third move deviations in the regular Spanish move order.