I think you may have your concepts a bit off. LPCM doesn't "support" anything. It is the decompressed audio signal that comes from a source device to an AVR or TV. LPCM can be sent in any number of channels.
Dolby Digtal, DTS, and all their variants are the compressed or coded audio signals that are sent from a source device and must be decoded, usually at an AVR but sometimes at a media streamer and blu-ray player depending on their features. I believe those codecs support up to 7.1 channels; however, I only think you can get up to 5.1 DD or DTS on a TOSlink fiberoptic audio connection. The HD audio codecs up to 7.1 can only be carried over HDMI due to the higher bandwidth required.
7.1 is really 8 discrete channels. The 8th channel is the subwoofer channel so it is called ".1" because it is not a full range channel. If someone is referring to 8 channels, they are probably referring to 7.1 audio.
The ability to support HD audio and 7.1 channels is a function of your hardware, not whether it is LPCM or coded.