My analog journey - time for a new phono stage or?

With help from members of the forum, several years ago I upgraded the cartridge on my then primary turntable. A year later I purchased a Musical Surroundings Phonomena II+ phono stage after demoing it at my house against a comparably priced Soundsmith unit. Last year I took the plunge and purchased from Upscale Audio a Rega P6 with a Sumiko Songbird low output MC cartridge. I purchased after demoing a Clearaudio Concept and the Rega locally, deciding Upscale was more knowledgeable than that dealer.

My virtual system can be viewed for all the details, but key components are the downstream Ayre Acoustics K-5xe preamplifier, Proceed HPA-2 amplifier and Aerial Acoustics Model 8b speakers. 

My issue is that I find that while the new turntable and cartridge definitely improved the detail/clarity of the sound reproduction, both the low and high ends seems to be missing complete extension and the soundstage is rather two dimensional, although instrument and vocalist placement and separation are very good and there is a seemingly clean background with no noticeable noise. I make these judgements compared to my digital front end, listening to the same albums/tracks on both. I don't necessarily expect to match the sonics of my digital gear, as I realize analog can be far more costly. FYI, I listen primarily to classical and jazz, some vintage rock, but typically acoustic music. My wife and I both play musical instruments and we attend live concerts, so we have a good handle on how instruments, bands, orchestras should sound and realize it is a fool's errand to seek to match the live performance.

I've read several threads on this forum and a number of review articles. A better phono stage may be an answer, emphasis on may. I experimented with loading and found the 121 or 150 ohm settings on my current phono stage work best. Below that and I lose high frequency detail. Above that and I end up with unacceptable sibilance on some recordings. FYI, the cartridge manufacturer calls for loading of >100 ohms, so my findings make sense. As a sidebar, I have come to realize how variable the quality of recordings and pressings are. The better TT and cartridge only emphasized this. 

So looking for more extension, deeper soundstage and a fuller, more natural sound lead me to a preliminary list of phono stages, with the goal of keeping within a budget of $2,500 or less. (I am agnostic as to solid state vs. tubes and will consider used gear from a good dealer or individual with happy customers.)

Pass XP-15

Whest Two.two or higher end model 

PS Audio Stellar Phono

Parasound JC Jr. or JC+

Allnic Audio H-1201

Aesthetix Rhea or Rhea Signature

Rogue Ares or Ares Magnum

Manley Labs Chinook - Upscale Audio's favorite around my budget

The list is long because there are thankfully many seemingly suitable options. I am open to others that would meet my goals and budget. I am hoping to hear from those of you who have auditioned or owned one or more of the above.

A few technical questions:

I have been sensitized to the need to match phono stage output to my pre-amplifier's input. One article I read suggested a rule of thumb that the input impedance of the pre-amp should be at least 10X the output impedance of the source. Is this accurate? FYI, my pre-amp has an input impedance of 20k Ohms on the unbalanced and 40k Ohms on the balanced inputs. So if the rule of thumb were correct, I need a phono stage with an output impedance of 1,000-2,000 Ohms or less.

The pre-amp, amp, my DAC and CD player are all balanced. While the Rega TT dos not have balanced outputs, I noticed that many of the phono stages have them. Is there a benefit to using the balanced outputs from the phono stage e.g. lower noise and greater gain?

Last question is whether my cartridge or cables from phono stage to pre-amp are a potential cause of the limitations I'm hearing. The cables are Transparent Music Link Plus 1.5m. I presume a more costly cartridge, particularly one with a line contact stylus could make a difference.

Where to invest the dollars??? Thanks for reading this long, detailed post.