My understanding of the difference between SL2000 and SLX is that they are the same product and SLX is the top tier/most full featured version. Would there be any reason to have both SL2000 and SLX in the same environment?
http://www.solarwinds.com/products/pricing/
http://www.solarwinds.com/documentation/Orion/docs/ScalabilityEngineGuidelines.pdf
SL2000 limits you to 2000 elements, where SLX is "unlimited" elements. The "unlimited" comes from the fact that you don't have to purchase this licensing individually for each APE you run. Typically, there is no impact to polling on a single engine up to 12,000 elements. Once you breach this quantity, you can start looking at adding some APE's at the cost of the APE, instead of APE + additional license. Theoretically, you can support somewhere in the vicinity of 100k elements on a primary + 9 APE's without purchasing additional licensing. Where, with an SL2000 license, you are limited, as stated, to 2000 elements.
-HTH!
