Given you really like the overall sound of the S5s and seem to mainly be after more visceral heft and bass punch it sounds like a pair of good subs might be just the ticket. Added bonus is your S5s with subs will likely be more full range with better bass than another standalone speaker in your price range, and the bass may even be better integrated with your room. I get that you like Rel, but Vandersteen subs are worth a look too, and they have some neat integration features and are also very fast so will likely work well with your sealed-box speakers. Best of luck in whatever you decide.
Anyone hear Vivid Audio Speakers? Considering Vivid Giya G1 Series 2 from Magico S5 MKII
Have new pair of Magico S5 MK II and have had Magico for a long time. I love them but considering trying either Giya G1 Series 2 or YG Acoustics Hailey 2.2 from my Magico's. Curious to hear from anyone that has head