There are several ways to trigger your Metz 48 AF-1...
1. Mounted on the camera hot-shoe. P-TTL and HSS are available, as the dedicated hot-shoe pins pass relevant information between the Metz flash and the camera.
HSS is supported if the camera mode is set to TV (shutter priority) or M (manual). Note that HSS is a setting specifically made on the external flash
("P-TTL HSS" on the Metz 48).
2. Remote (Off camera) via the built-in camera flash, set to wireless mode and the Metz 48 AF-1 set to SL (Slave) mode. Channels must be synched.
The Metz 48 must "optically see" the flash from the built in flash. You can set the built-in flash discharge method to "Master" or "Controller" (K-x, K-7, K-5),
but HSS is not available with the built-in flash (as you are limited 180/sec or slower). You do keep P-TTL functionality. You could also mount another specific external flash on the hot shoe of the camera.
The Metz 48 AF-1 does not operate as a Master or Controller. You would need to mount a Metz 58 AF-1/2 or equivalent Pentax flash on the camera (or via a TTL sync cable)
to keep P-TTL and HSS functionality.
3. Use a Pentax dedicated TTL sync cable to connect the camera hot-shoe to the flash hot-shoe. Hot-shoes have pins specific to the camera model.
Basically, you extend the physical connection between camera and flash via the cable. Can be very useful or a pain in the butt. Length is the issue here,
but you retain P-TTL and HSS functionality.
4. Radio controlled remote flash triggers. I have two sets of Cactus v5, but they will not pass P-TTL information, so I tend to use external flashes in manual mode, at least for now.
Most triggers operate as simple switches, but there are some rather expensive solutions for Canikon systems, none for Pentax that I am aware of. I can trigger the Cactus v5's either from the hot-shoe,
or by using a supplied cable connected to the sync socket on the left side of the prism housing of my K-7 and K-5.
The K-x does not have a sync socket.
(You can also trigger the Cactus v5 manually using the built-in button..., great when shooting in bulb mode.)
So, in the end I think your expectations are a bit high. You can invest more money for additional and more capable flash units,
but remember that you will be still be limited in range
when using remote flashes in "optical" mode. Any appreciable distance will require either a very long cable or radio triggers.
You can gradually expand you flash system and combine P-TTL flashes with radio triggers (that will trigger those connected flashes in manual mode),
but using flash shutter speeds (180/sec or slower) with HSS is mutually exclusive. HSS is not flash in the traditional sense, but rather a series of pulses (i.e., continuous light),
that start fractionally before the curtain opens and end just a bit after the curtain closes. HSS has limited application.
Here is a good link that explains HSS (FP/focal plane shutter) and other flash basics very well. The entire site is a good read.
Four Flash Photography Basics we must know - HSS 
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