I'll start off with the graphic. To help you with your bearings, south and I-280 are to the top. Downtown and CA-87 are to the left.
The ballpark is on the now familiar Diridon South site. Across Park Avenue is the fire training center, which is should be converted into a public park, perhaps with parking for some 600 cars underneath. The park could have a small playground and playing fields for soccer/football and baseball/softball. To top my wish list for the park, it should be named after the late Pat Tillman. I have to admit a bias regarding Tillman because though I didn't know him personally he was a contemporary of mine, but regardless it's hard to find a more fitting, interesting former San Jose resident for whom a park could be named than Tillman.
The soccer stadium is located on what is currently an equipment rental facility. The company owns several parcels spread among two blocks of Dupont and McEvoy Streets south of Park Ave. I've gone by there several times while checking out the Del Monte site, and I noticed that it's really underutilized. One parcel at the entry to the site is for sale. An office building in the middle of the facility is empty and has a for lease sign on it. There's a good amount of open space there. Neighbors include a couple of auto repair shops and a welding company. The area is rectangular in shape, and could accommodate a 22-25,000 seat soccer stadium with little trouble. If the street grid were realigned, a compact but spacious soccer stadium could work very well there. A partial roof would be required to help mitigate noise. Of course, there would be issues with acquiring the land and moving the equipment rental company, but that comes with the territory.
One small note: the PG&E substation has been realigned next to the ballpark (in grey). If this can be done (the amount of land is the same if not the shape), it would cut down on the potential costs associated with moving the substation.
I spoke at tonight City Council Open Forum about this site. We'll see if, like my suggestion to Oakland about the Broadway Auto Row site, anything comes of it.