There is an argument between the Rosh and Rav Hai Gaon. Normally when there is enough land for the males to inherit and the daughters to be feed then that is what happens. [That is to say that daughters and a widow do not inherit, but they do get feed from the proceeds of the land.] If there is not enough land for both the boys and girls then only the girls get feed. But if the sons sell the property the sell is valid. That is straight from the Gemara itself. But what happens after during the time of the Geonim there was made a decree that movable property is also used to pay for the Ketuba and all the conditions of the Ketubah.
That is where Rav Hai Gaon says after that decree now the girls would get feed from the proceeds of the sell. The Rosh disagrees.. The question that Rav Shach brings is that the proof that the rosh brings is hard to understand.
The Gemara says that there is a proof to Rav Asi that the boys have some rights to נכסים מועטים [small amount of land], because if they sell, the sell is valid. The Rosh brings this as a proof that they keep the money of the sell.--even after the decree of the Geonim.
I admit that I have trouble understanding the answer of Rav Shach to this question. It does look that you can not bring a proof from the sell being valid before the decree and the sell being valid after the decree that the boys might in fact have to feed the girls with the proceeds.
Basically Rav Shach is saying that the point of the Rosh is that you see there is a no "halot" settling of the land on the money, such that the money is in place of the land. We do see that with Maasar Sheni but not here. So while there is a decree to use movable property to pay for the Ketubah, that means money that was actually inherited. Not money that came because something that was inherited was sold.
