First lets start by saying this book (as far as I know from googling it) is about stocks (and or futures). Not a forex book, although information can be gained from it not all of it applies, infact the first passage dosnt apply at all.
While googling upstairs trader found nothing, I did find this at
http://www.bizterms.net/term/Upstairs-market.html:
"Upstairs market
A network of trading desks for the major brokerage firms and institutional investors that communicate with each other by means of electronic display systems and telephones to facilitate block trades and program trades. "
It could be assumed that an 'upstairs trader' operates in the 'upstairs market' on the other hand this article from investopedia may help:
Upstairs Trade
I'm really not sure on that one!
For the liquidity section/quote (the first one) I'm not sure on the lingo, but it sounds like what hes saying is he will close half of his positions just before, and half just after to equal to being at the same price, versus trying to deal with the liquidity issues and timing that the market will present when everybody else is doing the same thing.
For the second paragraph, again this is just a guess but, if I remember correctly it sounds like hes dealing with options. With options you have the option to deliver a contract, eg make a purchase. Its kind of like buying the right (or selling the right) to buy at a set price, and then if you want you can buy it. Its kind of like a market on top of a market. The price varys and you can make money with just options, but... its similar with making it with the market. Now I could be wrong, its beenawhile since I researched options, they are of no use to me in the forex!