Your surround processor should work as a preamp for the amp you are considering. However, please be sure to check that the output impedence of the processor is much less (e.g., 5-10 times less) than the input impedence of the amp.
Chances are that you will not be able to use the surround processor for the turntable. You will likely need to purchase a phono preamp. The output signal of many cartridges are much smaller than the output signal of other devices such as a dvd player, tuner or cd player. Phono preamps are often necessary to boost the signal sufficiently for a line preamp (or processor) to utilize. Further, phono preamps are also designed to handle the output impedences of various cartridges -- you will need to check and potentially adjust settings once you select the cartridge and phono preamp.
Others can speak better to two amps feeding the same speaker, but I would be cautious about that since the closed loop would also mean that each amp is feeding the other amp. Even if the power is off on one amp, there may be some complete circuits in that amp via the speaker cables and output stage of the amp. Other audiogoners may have experience and knowledge here that refute my concerns, but I would be very careful with driving a speaker with two amps unless there's a switch to disengage one of the amps speaker wires while the other amp is active.
There are a number of systems fellow Audiogoners have listed that combine both two and five channel listening in one system. You may wish to peruse some of those systems for some ideas.
If memory serves, one option is to utilize only three channels of the surround sound amp (rears and center) and use two channels of the stereo (e.g., valve) amp all driven by a single five channel processor (i.e.,preamp). That requires some thought to amp matching, but many processors allow for separate volume controls per speaker pair so the volume matching could be pretty simple. It does mean that two channels of the surround amp go unused. When listening to music, simply switch the processor to stereo mode (this may still require a separate phono preamp).
Chances are that you will not be able to use the surround processor for the turntable. You will likely need to purchase a phono preamp. The output signal of many cartridges are much smaller than the output signal of other devices such as a dvd player, tuner or cd player. Phono preamps are often necessary to boost the signal sufficiently for a line preamp (or processor) to utilize. Further, phono preamps are also designed to handle the output impedences of various cartridges -- you will need to check and potentially adjust settings once you select the cartridge and phono preamp.
Others can speak better to two amps feeding the same speaker, but I would be cautious about that since the closed loop would also mean that each amp is feeding the other amp. Even if the power is off on one amp, there may be some complete circuits in that amp via the speaker cables and output stage of the amp. Other audiogoners may have experience and knowledge here that refute my concerns, but I would be very careful with driving a speaker with two amps unless there's a switch to disengage one of the amps speaker wires while the other amp is active.
There are a number of systems fellow Audiogoners have listed that combine both two and five channel listening in one system. You may wish to peruse some of those systems for some ideas.
If memory serves, one option is to utilize only three channels of the surround sound amp (rears and center) and use two channels of the stereo (e.g., valve) amp all driven by a single five channel processor (i.e.,preamp). That requires some thought to amp matching, but many processors allow for separate volume controls per speaker pair so the volume matching could be pretty simple. It does mean that two channels of the surround amp go unused. When listening to music, simply switch the processor to stereo mode (this may still require a separate phono preamp).