Adding a preamp to HT setup

i Have been convinced that adding a good preamp with HT bypass to my system will improve my 2-channel listening experience. I have read multiple threads here, and reviews all over, and there is an overload of information.

the 2-channel system is Aerial 7T’s, Odyssey Stratos amp and Oppo UCD205 player (I still use discs), and I’ll feed streaming in to the Oppo from the Marantz pre-pro. No vinyl.

the room is 19x12x8, and ‘live’, hardwood floors with a rug, drywall all walls. The rear of the room is open to the kitchen.

the improvements I seek are in soundstage focus and solidity, along with depth. Greater resolution of detail (love the little things that come out of recordings that make it real), and air around performers. All the things that draw us into a performance and involve our emotions.

i have an interest in what tubes would bring to the party, but I have no interest in spending all my time swapping out tubes to tailor the sound, I just want to listen to and enjoy the music. 
HT bypass is a must, obviously, and I’m curious about the lifespan of tubes given that my ‘normal’ everyday use of the system includes tv/movies where the pre won’t really be involved, except to pass the signal. I don’t know if there is an option for a pre amp to pass the signal through when not turned on, but that would be my preference.

Music interests range from Dire Straights, Pink Floyd to The Tenors/Josh Groban, to instrumental guitar...vocals and instrumental realism are big for me.

im comfortable buying used to stretch dollars, and would like to keep it below $2K, but would double that if convinced it was worth it.