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

No disrespect to Klyne Audio. That was not my intention on my earlier post. I've not heard their preamps but over the years I have read many great things about them. I'm sure they make a great product. What I was trying to imply is the SF Line-2 is no slouch. I am fortunate enough that we have two really nice local shops that have been around a long time; one a relative of mine owns and one I worked part time at years ago. Both stores let me take gear home all the time and that has been great for me to educate myself and train my ears. Between the two stores they have sold most known brands including the former Sonic Frontiers, Pass Labs and Revel so I know this gear well. Lived with a Sonic Frontiers pre previously and have a Pass amp, so I know this product well... very well.

Back to your original post... Your Line-2 is more than in the league with your Revel M106's. Careful I am not saying the M106 is not a nice speaker because it is, but I have heard the Line-2 on bigger Magnepans, Thiels, and Vandersteens with Levinson, Classe, Sonic Frontiers and Conrad Johnson amps so I know it can hold its own even today. The Line-1 is a very nice preamp as well  and I have heard it on the same speakers including Dunlavys, and ProAcs; my father has ProAcs and his Line-1 is more than adequate with his ProAcs and ARC tube amp.

Is the Line-2 in the same league as a Pass XA30.5? Well I would say again it will hold it's own just fine but Yes the Pass is the better piece; anyone who argues that is being silly maybe. If you tweak your Line-2 a little as I mentioned in my earlier post you will hear the benefits through the Pass. Also if you are getting the XA30.5 or any Pass amp you are wasting your money if you don't run it balanced so no matter what you do with your Line-2 or get another preamp because you have the bug to upgrade I would strongly inform you to use a balanced preamp regardless if it SS or a Tube design. Likewise if you are not using balanced cables on your Line-2 now you should be because it will sound more open; it's not something you have to really concentrate on to hear - it will be obvious with decent cables. I agree with someone above the cost of sending it in for an upgrade may not yield much of an improvement but other tweaks will.

I would recommend to make sure the rest of your system is up to your Line-2. What is your source components, cables, and etc.? If you don't have dedicated circuits to your equipment I would do that as the Pass will not come to it's potential it has to offer; my Pass was thin sounding until I ran dedicated lines. If you can't run dedicated lines I would still change out your receptacles to at least some nice Hubbells. Maybe you have done all this, but if you haven't you haven't heard what your Line-2 can do or the rest of your system. Give your Line-2 a chance on the XA30.5 before you ditch it. Only downside I do have with any tube preamp or any tube equipment is tubes go bad and there is a cost maintaining them.

I wholeheartedly agree both SS and Tube camps offer great equipment; both can be great. I believe its all about synergy as one piece might work great on one system but not another.   Good Luck.

What are you using for an amp currently to rule your Yamaha receiver is more transparent than the Line-2? I can't imagine any receiver especially a $250 AVR has a better preamp section. Not sure if you're cranking the treble on the AVR giving it more brightness it seems to sound better or what is going on.

You mentioned you replaced the tubes; did you do them all and do you have any means to check them. I have an older Arcam AVR and it's ok and my father has a much newer higher priced Marantz AVR, but it's no where near his Line-1 in performance and your Line-2 should be even better. Maybe that Yamaha is just a giant killer?

I bet the 508.24 still holds its own. I wouldn't rule it out as not being a nice performer with all the gear you are discussing. If you are running some 25 year old cables I'd invest the money there first, or if they are new but the entry level of whatever brand, you should experiment with proper cables. This gear should sound really good with nice cables.

The 508.24 was a well regarded player. Sure newer players have improved and maybe an Oppo 105d makes sense if you're system is mixed into a home theatre set up as well. Agree you might be better spending money on your source than your preamp, but I wouldn't get in any hurry.

Hopefully you have a tube tester  or have a shop locally that can test your tubes and put the Line-2 on the bench to check it out. Something just doesn't sounds right if you're preferring your Yamaha. If you have your Line-2 plugged into some A/V power conditioner with your A/V equipment trying plugging it directly into the receptacle; same will be true with the Pass you have coming.

Best of luck