I think of the sound from this rig as having no gaps in it...no annoying frequencies that you can't dial out and just very musical wherever you set the controls. I don't think there's a bad sound in that amp..or at least I've not found one yet!
I've had a couple of sets that sounded slightly unbalanced at first, but they quickly settled in after playing. My most recent set were good straight from the pack though.
TI flats are my favourite strings. Once you have used them for a while it's hard to enjoy playing anything else! I liked the LTF strings also, but were a bit too mellow for me. TI's just seem to work so well with my Jazz and Precision basses , they have a certain mid range thing going on that sits so well in a mix.
https://reverb.com/uk/item/42144898-jt-amplification-alpha-direct-box-standard
I can recommend the JT Alpha Di. I've had mine a while now and I wouldn't be without it now. Great bit of kit.
Save yourself some money and get one of these instead. Great bit of kit and mine arrived in about 10 days from what I remember.
https://reverb.com/uk/item/42144898-jt-amplification-alpha-direct-box-standard
The Ampeg pre amp is really simple but effective and makes perfect sense to me. Like you say , it just works. I don't think you could make that amp sound bad , just dial in what sounds good to you and enjoy it.
Last couple of gigs I had the master at 3 o'clock (3 quarters up) and gain at about 10 o'clock. I cut the bass slightly, boosted mids (800) and slight treble boost...this was pretty loud for a mid sized room , punchy and quite clean. I always use the gain to set the overall volume level.