Piano strings have an additional feature that used to be commonly available in sets of bass strings.
They have no windings over the saddle. This means that it is just the core wire of each string is fixed at the saddle thus leaving the strings a little more free to vibrate. With these you can get close to piano tone with careful adjustment of technique and eq.
Combined with multi-scale, you could get even closer to piano tone.
Piano wound or Superwound bass strings, as they are sometimes called are not so commonly available now.