Hyperion HPS-938 speakers

First, I have no experience with these speakers. However, I've learned to always look to the amplifier/speaker match as one of the keys to a satisfying or unsatisfying system. Amplifier-speaker synergy is paramount. If the match is a poor one (a mis-match), and synergy does not exist, you never hear the best the amplifier can offer, nor the true potential of the speakers. It sounds like you have a mismatch and lack of synergy there. If my theory has merit, you need to look to speakers that are known to match well with Arcam gear, since you have an all Arcam system. In addition, I may be wrong, but don't some of the Nordost cables have a lean sonic signature? Good luck in uncovering your system issues.

Different experiences and performance with the same speakers or same line of speakers means one thing. As with all speakers, their performance is highly dependent on the associated electronics, front end, wires, room, AC, isolation, etc. -You need SYNERGY-

Based on the high opinions of your speakers, Hawkeye43, I'd keep the 938's and build a new system around them.