I have Vector Research VRX5200 R analog receiver (very old) and was wondering what is the best way to connect my Klipsch center speaker without buying a new receiver. Right now I have 2 front Infinity (bookshelf) speakers
Diagram #2 on this site; http://kantack.com/surround/surround2.html is a version of the old DynaQuad circuit. You should have a volume control pot in the "+" line to the center speaker to allow matching levels.
Quite honestly, I wouldn't try this with a Vector Research reciever. If you have placed no value on the receiver and plan to ditch it when it fails, here's your oppportunity to buy a new receiver with Dobly Pro Logic built in - then you'll have a center channel output. The Vector products were low end and not well suited to driving multiple speakers. This circuit represents what most amplifiers see as a deliberately shorted front speaker circuit. I can't tell you this connection will place too much stress on the amplifier and cause a failure but, if it were me, I would be looking at a more stout amplifier for this experiment than a Vector Research. This connection tends to work well with transformer coupled outputs - the Vector is direct coupled (more or less) - where the transformer acts to protect the amplifier's outputs. Even then this is a dodgey affair and not recommended for most modern receivers or amplifiers.
If you want to pursue this to a more satisfactory conclusion, buy another matching center speaker and run them as shown in Diagram #1 with a pot (or better yet an L-Pad) for level adjust in line. Depending on the speakers, this might work well but it would certainly place less stress on the amplifier than a deliberate short would.