I own three stations, use Simian at all three. Two are satellite, one is live/music on hard drive.
You do not need the expensive ASI card, but you should get an ASI sound card. The reason is that the ASI series of sound cards comes with a virtual mixer in its software that Simian uses to make smooth transitions from audio file to audio file. There are two inexpensive cards that will work: the ASI 5111, which is a PCI card that runs around $450, and the ASI 5211, which is the PCI express card, which is about $550.
You mentioned that you plan to upgrade the computer--you will find most computers no longer have PCI slots, so plan on buying the ASI5211. We just upgraded our production room computer--found a off-lease Dell at Microcenter for $400 with a big hard drive. Important things to look for:
*Lots of RAM, Simian looks ahead and loads the upcoming items to be played into RAM, so if you are using music from hard drive, you will need the RAM;
*Satellite or Music on HD?--determines the size of the drive. We have a terrabyte hard drive on a machine used on the live music station;
*Note that Simian will not run on a 64 bit Windows 7 installation. There is a free download from Microsoft that creates a virtual 32 bit operating system for Windows 7; or you may be able to find an XP pro install. I have my doubts that Windows 8 could run a lemonade stand.
Satellite fed formats: BSI will sell you a little blue 24 trigger USB device--it is made by Measurement Computing. It's USB 1024 LS, controlled off the USB bus. I use these devices instead:
http://www.mccdaq.com/usb-data-acquisition/USB-DIO24-Series.aspx
Which is the same device, but with a 37 pin connector you can use to connect your incoming trigger lines ("net cues" or "relays") from the satellite receiver. I buy a plastic Hammond box from Mouser and mount the card inside the box--makes for a much more stable installation.
You can also connect these devices to a relay panel (also made by Measurement Computing) for various switching functions. On one station we have a console where channels can be turned on and off remotely. We have 5 different satellite feeds which we run into five different channels (leaving the faders up), and use a relay board to turn channels on and off as needed. This simplifies, for example, switching between our Dial Global AC feed to Delilah from Premier Satellite. This is the "relay rack" function of Simian, you program macros to turn on or off the particular relays, or use the time command functions (we use this to join Fox News TOH).
Broadcast Tools makes a device that will accept triggers and issue relay commands, this is a serial device (you can use a USB to serial adapter to control it, since serial connections have vanished from most computers). If you have very complex programming, they also make a 32 line trigger input device. Somewhat more tricky to get to work, but the current version of Simian supports it. I have one on my AC station, with all 32 trigger lines in use.
You will find that Natural Log and Natural Music work great with Simian. We have two different locations, the logs are just e-mailed from the main office to the other station, where the afternoon guy loads it in for the next day.