Mike, I have a standard Line 3 that came with current production 6H23s, not sure what make. I replaced the two rear outside tubes with Amperex 7308s. With the stock tubes in those positions the Line 3 sounds lean, and has an annoying glare in the upper mids/lower treble. The 7308 added a fullness across the spectrum, eliminated the glare (without rolling off the highs), richened the mids, and increased bass extension and articulation. I also tried replacing the rear inside pair with NOS Jan Philips ECF82s, recommended by Kevin Deal. The tonal balance sounded very life like, however they also reduced the sense of layering and air in the soundstage.
I haven't tried rollerblocks, cones, etc. I have had very good results with TG Audio HSRa II, and now HSR SLVR power cords.