I have pretty carefully read your posts. I relate to your perspective on music playback. Until recently I was a working musician and have made a living as an audio consultant and dealer. I own one of Nelson Pass’s “kitchen table” creations, the M3. Believe the SIT-3 is one of his better works. And there are two main issues, as you mentioned. Speaker and amp combination are the “two hands clapping” in any system. And the preamp is “the heart”. Central is your feeling of how the music sounds. If you like the Maggies you are not going to get that open sound from any other speaker that works for you other than a legendary pair of Quad 57s. It is counter intuitive, but if the SIT-3 and the .7s work for you they work. But the First Watt should be an excellent match with the 57s. I would save your money and stay with what you have. BTW you have one of the best TTs for $2k out there in the MoFi. And the your digital is said to be terrific although I am not a digital guy. An excellent phono stage and, according to TAS Editor’s Choice for many, many years as “the best at any price”, is the Audible Illusions preamp. The model with the phono stage is the M3A or M3B. I own and adore my M3B. A new one is $5200. But you can get 90% there with a factory refurbished one for around $2500. One of the fortes of the AI is that they are a SET design using only one tube per channel for the preamp and for the phono stage. And a SS amp is normally smoothed off by a tube preamp-let alone a SET. I know Dan Wright very well. I did an audio show with him. You can’t go wrong with one of his preamps but I prefer the AI. Unfortunately, a SET amp is a bridge too far for the Maggies. I am an all SET guy for life. Unmatched musicality with the right speakers. As good as the First Watt is, it is still a “sand amp” and has a SS sound.
But if all those wonderful reviewers and YOU love this combo, stick with it. Some day, or now, you may want to get Quad 57s. I joyfully lived with my 57s for 10 years and still miss them. But something you don’t get with 57s or .7s is dynamics and slam. This can be helped by adding a subwoofer. I would only use a Rel. They only make subs and they hook up directly to your amp making for the best connection. Surely, you may be more able to better push the Maggies with a higher power amp but adding an AI will give you substantially more gain and adjustable gain for MM. Matching amp with speaker is about the toughest thing in a system and if you, mostly, like what you have, be happy! Some day, you may want to get a SET. Ultimately, there is nothing that compares. SS amps try to sound more like tube amps and multi tube amps are trying to sound more like SETs... mostly.