A number of things to consider here.
1. What is the distance from the studio to the transmitter site, and what is BETWEEN the studio and transmitter? If you are in Kansas where the highest thing on the horizon is a grain elevator, probably no problems unless you have a long distance between the two sites. However, if you are in hilly country, you may quickly discover why the internet was used to get audio to the transmitter.
The STL's microwave frequencies don't go through hills very well. If there's a big hill between your studio and transmitter, you may need a big tower at the studio, or even a two-hop link (one to the top of that hill, then another to the transmitter).
Here's a site that can give you an idea of the path between studio and transmitter:
http://n9zia.ampr.org/path.main.cgi If the path looks at all marginal, get professional help before you go much further. You can find the coordinates for your transmitter site at FCC.Gov; Topozone or Google Earth can give you the coordinates for your studio, Topozone will show you the elevation at your studio.
2. What kind of transmitter? Many imported transmitters have this built in stereo generator design, (seems to be a European thing). However they usually have jacks that allow for a composite or multiplex (i.e., stereo audio) to be fed into the transmitter part directly, bypassing the stereo generator.
Depends on what you have for audio processing now, and your budget, determines which is the best way to go. If you are happy with the present processing chain (or can't afford new processing), then you will have to use what is called a "discrete" system, where the left and right audio channels are sent by separate STL transmitters. The only STL equipment commonly available to do this is the Marti STL-10 systems. They are available new from the usual equipment suppliers; or you can find them used. E.G.:
http://bohnbroadcast.com/forsale/stl.htm. Used STL-10 systems, if refurbished, can be very reliable, and can save you $$$ over new equipment without any compromise in quality.
If you have the budget to improve processing, you have more options. For example, compared to sending audio straight into the stereo generator of the transmitter a reconditioned used Optimod 8100 can sound very good. They're often on E-bay for around $1k or so. Or you can go up from there. If you want the processor/stereo generator at the studio, you would then need a "composite" STL system. Instead of two transmitters and two receivers, you then have one transmitter receiver combination that is "broadband" in that it will pass the complete stereo signal (and add-ons such as RDS) directly from studio to transmitter. New prices for composite systems run from around $4K to $6K.
Before buying used composite STL equipment, best to consult with an engineer familiar with the equipment. On some of the used equipment it is difficult to change frequency, even if advertised as "frequency agile." (E.G.--older TFT 8300 series). Other models are no longer accepted by the FCC, or have obsolete transistors that can't be replaced.
3. If you are satisfied that you have a clear path between studio and transmitter, and have decided whether to go "discrete" or "composite," I would recommend Terrestrial RF to do a frequency study, the required "prior coordination notice" process, and preparation and filing of the FCC application.
The "PCN" process, as it is sometime called, requires notices to be sent to everyone who have STL stations on your selected frequency and the adjacent frequencies--over a wide area around your station (250 miles on channel!). Something no sane person would attempt without help.
www.rflicensing.com/
4. As you can see, there are a lot of questions to be asked and answered before you even get to the coordination process.
