Tom,
What model is the receiver? If it is an HT receiver which supports mains, surround and center speakers, I'd be surprised that it doesn't have some type of sub output. Are you sure there is not an RCA out for "LFE" (low frequency effects), which is sometimes what the sub out is called on an HT receiver.
Does your receiver support Dolby Digital 5.1 surround sound? If so, it must have a sub out of some kind.
TIC
What model is the receiver? If it is an HT receiver which supports mains, surround and center speakers, I'd be surprised that it doesn't have some type of sub output. Are you sure there is not an RCA out for "LFE" (low frequency effects), which is sometimes what the sub out is called on an HT receiver.
Does your receiver support Dolby Digital 5.1 surround sound? If so, it must have a sub out of some kind.
TIC