UPDATE:
I just wanted to give all of you that took an interest in my project an update. I purchased a 'new to me' Shitt LYR 2 headphone amp and a pair of Hifiman HE-R9 cans. To sum it up, I couldn't be happier for a first time setup and came in under $1000 CDN.
The amp and headphones sound fantastic. There are two tubes in the amp and they have a great sound. As a bonus, I don't have any of the interconnect hassles I thought I might have.
RCA Output 2 on my preamp ran directly to the line inputs on my SVS SB-2000 Pro sub. I plugged these directly into the line in on the LYR 2. Line out on the LYR 2 goes to the sub. When the headphones are connected, the inputs to the sub disconnect by themselves automatically.
The only manual step I have to do is turn off Output 1 on my preamp that feeds the balanced input to my power amp.
The HE-R9 can kick out a lot of bass that I like with the 60s and 70s music I enjoy.
Prior to all this, I did have a set of Bose BT ANC headphones. You know what they say, 'no highs, no lows, must be Bose'. Anyway, there is no comparison. I was looking for a hi-res audiophile type solution for home and am satisfied with my start. Knowing me, now I will want to collect headphones and an open-back design will be first on my list.
A lot of your opinions factored into the direction I went so my thanks goes out to your knowledge, experience and willingness to help.