Mdemaio, in your situation you want an amp and speakers with play well at low levels & have excellent inner detail. Based on your musical preferences (which are similar to mine), for an amp recommendation i'd look at a 2nd hand Modwright KWA-150. The KWA-150 sounds great played at low levels thanks to its resolution and wonderful inner detail. It also sounds warm & tube-like, yet clean which I think would suit jazz, classical & world well. It also has good control for rock music. The last guy selling one on the 'Gon was asking $2800 obo. A 2nd hand Modwright LS-100 pre would be a good option for preamp. A good example recently went up on the 'Gon for $1800, so for around $4500 you'd have a great value pair of amps able to play wonderfully at low level. That also gives you an upgrade path as you could later upgrade the tubes in the LS-100 to matched NOS tubes & send your Oppo to Modwright to get the tube mods done.
For a speaker recommendation, if you are mainly listening at low volumes, I would recommend a pair of Josesph Audio Pulsars placed on stands. A nice pair recently sold on the 'Gon for $4495. For a floorstander, for similar money 2nd hand i'd recommend Living Voice OBX-R2's which are lovely sounding speakers & well suited to your requirements. The only Harbeth speakers I could recommend would be the 40.1's, however the last pair sold here north of $7500.
For acoustic treatments, i'd look for a good value proven product. I've heard good feedback about the Vicoustic products. But possibly the most universal and easy to place room treatments are the new Stillpoints Aperture panels. Not cheap at $600/panel, but you only need 4-6 to start with then you can add more later depending on how your room measures. Hope that helps! ps: this post took way too long.
For a speaker recommendation, if you are mainly listening at low volumes, I would recommend a pair of Josesph Audio Pulsars placed on stands. A nice pair recently sold on the 'Gon for $4495. For a floorstander, for similar money 2nd hand i'd recommend Living Voice OBX-R2's which are lovely sounding speakers & well suited to your requirements. The only Harbeth speakers I could recommend would be the 40.1's, however the last pair sold here north of $7500.
For acoustic treatments, i'd look for a good value proven product. I've heard good feedback about the Vicoustic products. But possibly the most universal and easy to place room treatments are the new Stillpoints Aperture panels. Not cheap at $600/panel, but you only need 4-6 to start with then you can add more later depending on how your room measures. Hope that helps! ps: this post took way too long.