Upgrade my Sonic Frontiers Line-2, or buy a used solid state Pre?

I don't think I explained myself very well. Previously, I had 508.24->SF Line2->Meridian M20 mkii active speakers (all RCA interconnects). A speaker died, and I decided that I got my money out of them after 24 years of use.

I bought the M106 (for $1300 with stands included) because I feel floorstanding speakers that cost under $2k are usually colored sounding, presumably, due to the cabinetry. I had a shot at dealer demo pair of Sonus Faber Venere 2.5 for $1500, but they just sounded overly colored and off to me. I heard the Wilson Sabrina in the same exact spot 5 days later and there was no such coloration (as expected), so my instincts were right there. I decided to go for quality monitors and good amplification over a larger speaker with so-so amplification. I figured I'm getting the same speaker technology as the well regarded F206 and F208. I have a lot of confidence that Revel has some serious engineering capabilities and put a lot of effort into the Performa3 line. I don't feel like they tried to cut corners or tried to squeeze 30hz out of a poor, lone mid-woofer. The one minor exception to this is that I suspect their choice of aluminum tweeters was to keep the Performa3 model from sounding too close to the Ultima line. So far, I'm really happy with them. Amazing quality for the price I paid.

Currently, I have the 508.24 (RCA)->Yamaha AVR->Revel M106. I have no amp, so the SF Line-2 is sitting on the shelf. To be clear, the line-2 has never been in the signal path with the M106 speakers.

The current setup is definitely more detailed than my original. I was surprised by this since I'm using an AVR.  It doesn't have the soundstage and the midrange is kinda flat, but the bass and high end are more revealing. I can hear voices fade away more clearly, even though they don't have the weight and presence they should. None the less, it's pretty amazing how far some AVRs have come. They used to sound really awful. The Yamaha seems to err by omission.

Finally, to the point, I'm dropping in two pieces (existing line-2 preamp AND xa30.5 amp) simultaneously into the mix next week (along with XLR cables and larger speaker wires). Hopefully it sounds amazing.

Well, I've had my rig put together for 5 days. The amount of detail is exceptional. I think at this point, my room is the weak link, so I begin the process of trying to treat our main living room while maintaining the WAF.

There is some fine grain, and if I were a betting man, I'd point my finger at the preamp. That aside, it's still really good. I do have some background noise when the preamp comes online. I'll probably send it in for the Signature Plus upgrade some time in the future to lower the noise floor.

I'm liking the XA30.5. The speakers could handle more power and sound even better, but I can't afford 150W per channel of Pass XA quality amplification. It might be my imagination, but when I turn it up loud enough that it starts moving out of class A, it sounds a little more lively and powerful. I noticed this particularly on "You can call me Al" from Paul Simon. However, if I listen at much lower volumes for awhile, some louder instruments or passages will give me the illusion that what I'm hearing is actually loud. I think that must speak to the dynamic ability of the amp. I'm really pleased that it sounds dynamic at lower volumes.

I wonder how something like an X250.5 (approachable) or X350.5 (a reach financially) would sound in my system at low to moderate volumes. Does a 350.5 sound similar to an XA.5 when it's in class A?

Maybe, but I suspect the XA is a little more refined regardless. My Aerial's require a lot of power so I'll stick with the X series. Can't recall if you're running balanced cables from the SF to the Pass as that will lower the noise floor. My X250 is a little noisy but not much even running balanced; it's not my preamp. If you're running a shielded PC on your Line 2 see if you can get a non shielded PC like a Kimber PK10 Gold or whatever they renamed it. The Kimber works great on SF preamps... you'll be amazed.

I am running balanced all the way through. I never noticed the noise on my old system running single ended, but maybe the 6db boost in the balanced circuit has brought the noise to light. The background noise was always very noticeable on my line-2 through headphones. It's definitely the pre. Everything is dead silent until it engages its output circuit. Parts Connexion told me it isn't uncommon, and that the new volume controller will zap the noise.