finding the weak link

Your speakers go down to 28hz. You will be surprised at how much more info will be extracted from your main speakers when you ad a subwoofer. Add 2. You won't be disappointed. my speakers are rated to 20hz. yet the subs were probably my biggest improvement.

then your phono preamp is not up to the task. Do NOT underestimate the importance of a GOOD phono preamp. The OL Silver arm is OK and actually hits above its price level as ALL the OL arms do. At some point you might want to upgrade to something like an Illustrious which is supposedly their sweet spot.  I have one that I bought for my Teres TT as a temporary arm. That was 12 yrs ago. I just upgraded to a TriPlanar. Yes it was better. But the OL has absolutely no shame when placed alongside the Tri. keep your eye open. i have it on good authority that there will be one for sale sometime soon. You have a good system in the PL and speakers. i would not consider changing the PL until you take care of the problems I mention.

BTW, like others have said, the KT66 & 6L6 tubes are something to consider. My own favorite is the 7581 tungsol. Fantastic freq response and the prettiest blue glow you have ever seen. They have the same specs as the KT66 as I understand

@rhach 

Addendum

I rarely disagree with @ghdprentice but will do so somewhat this time. I will agree that the PrimaLuna is not the last word in high end audio and integrateds may have some compromises that aren't made in separates. At some point, you will want to go up the ladder to separates. But I'd also note that the PL is the Dialogue Premium which is their top tier with better parts. This is why I would not switch out the PL just yet.. IIRC, the phono preamp he has now pulls double duty and costs around $500. Price doesn't tell the whole story but it tells a lot of it. This is a starter phono preamp IMO and the reason I put it as second in the list of upgrades just behind the subs. I am partial to Rel because they integrate very well and bring a lot to the mains as well.. But, if you have the means, then certainly upgrading the PL is a worthy consideration. But it is my  preference to only upgrade one thing at a time. That way there is little or no confusion as to what caused any sound difference

@rhach 

Very nice. The Manley Chinook is supposedly a great bang for the buck. Kevin Deal really likes them. I have never heard it but I trust the opinions of those who have them. You should be very happy with that upgrade

FWIW  I'd wait a couple weeks to let the Chinook get broken in before putting the sub(s )in the chain. This will help you identify  just how much improvement it did and then enjoy the sub. It should provide another thrill as well

Let us know how you like the upgrades