Upgraded power cords on active speakers is efficacious. I have tested such things out. Power supplies, amps, etc. in speakers respond to PCs.
I encourage you to think of your query as being resolved by working with entire sets of cables. Reports of how the LS50 reacts by swapping one PC will be of marginal value to you if it was used in a mixed set of cables. This is how the majority of audiophiles operate, and without particular discussion of the rest of their system, there is no way to isolate what the PC might be contributing.
Your best solution for advancing your rig in a meaningful way in terms of not only that PC, but all cabling is to attempt comparison of entire sets. This is true for all audiophiles, ones with active or passive speakers. Yes, this is more time consuming, more bother, and potentially more costly, but it is the only way to directly move the rig toward a desired outcome. All other mixing of cables is guesswork. Once a preferred set is selected, then fine tuning is advisable with one or two cables. This is more bother, more time consuming and potentially more costly, but it is the only way to move a system with certainty toward one's goals. Treat the speaker as any other part of the system in terms of cabling.
I encourage you to think of your query as being resolved by working with entire sets of cables. Reports of how the LS50 reacts by swapping one PC will be of marginal value to you if it was used in a mixed set of cables. This is how the majority of audiophiles operate, and without particular discussion of the rest of their system, there is no way to isolate what the PC might be contributing.
Your best solution for advancing your rig in a meaningful way in terms of not only that PC, but all cabling is to attempt comparison of entire sets. This is true for all audiophiles, ones with active or passive speakers. Yes, this is more time consuming, more bother, and potentially more costly, but it is the only way to directly move the rig toward a desired outcome. All other mixing of cables is guesswork. Once a preferred set is selected, then fine tuning is advisable with one or two cables. This is more bother, more time consuming and potentially more costly, but it is the only way to move a system with certainty toward one's goals. Treat the speaker as any other part of the system in terms of cabling.