Confused: Should I Upgrade Cables or Amp first?

marktomaras;
 Thanks for the explanation. I'm expecting the Parasound Halo to arrive from Audioadvisor on Thursday, so my plan is to first evaluate its effect on the system, then take it from there. I will bear in mind the possibilities you've kindly detailed. 

Wrap-up: I ended up sending back the Parasound Halo. I wasn't willing to keep it in my system for 150 hours to see if I would like it in the long run. Frankly, my current Jolida tube integrated, tube CDP and Silverline speakers all sounded very good to my ears right out of the box and only improved with break-in, whereas the Halo sounded very thin and generally unappealing to me. It's garnered many enthusiastic pro reviews, so I'm not going to pass judgement on it-- it simply wasn't a good match for my expectations and patience level. Another factor was that I borrowed  Margules hybrid integrated that was nearly new, and liked it  so much better than the Halo. The combination of muscularity and smoothness wrought by more power and a tubed pre-amp section was truly seductive. More power is good ! The Margules demonstrated convincingly just how much an amp can improve my system's sound. My wife prefers the pure tube sound, though, so I've decided to demo a Jolida 3502S-- a hot-rodded version of my current integrated that has the flexibility to use EL34's, 6550's, KT88's, KT120's, or KT150's.  The Jolida with KT150's would boost the power from 50 to 85 watts and based on my familiarity with the Jolida sound, it should satisfy both of us. So, in the end, I've answered my original question; I'm going with an amp. Thanks for everyone's input!

I drive a pair of Silverline Preludes (supposedly 91db efficiency but measured more like 89 in a Stereophile review…Silverline exaggerates their specs a bit it would seem, including the silly 35 hz bass claims for my speakers…35hz with the Preludes is just silly…I've measured it ) with a "factory upgraded"  Jolida 502p that puts out maybe 65 watts or so per side, and it kicks butt. My speaker cable runs are AQ 10' Type 8 that sound amazing, and likely would work at 20 feet if they had to. Great cable. Based on my experience with Jolida I bet the 3502 that appears to replace the 502 in the Jolida lineup is a GREAT amp. The only thing wrong with Jolida is they're relatively inexpensive so amp snobs diss 'em. Meh…(my 502 has been abused daily for years and works like new…I've compared it to much more expensive stuff and it shames some well regarded amps that cost 5 times as much). Over the last few years I've scored two excellent REL subs on Ebay at different times for around 200 bucks each…from the same era…a Q150e and a Q108e II, and they take up very little space but provide a much more realistic full range sound that I can't imagine not hearing now that I have these things (well, I can imagine it as I sometimes turn 'em off just to see what's what…and turn them back on immediately!).  REL 108s show up online fairly often and if you don't have room for one of those you simply have too much furniture.

At least the Parasound experiment was an easy one to decide, hopefully the KT150 will be all you need.  I've been chasing that last 5% of audio bliss, and am realizing that it's just not worth the trouble.  Get a sound that you like and enjoy your music!

wolf_garcia: Yeah, I sure hope it's "amazing"!  The 3502S is upgraded from the stock model 3502, which is just as well, as I'm used to listening to a modded 302. A rel sub is definitely something I'm keeping in mind for the future, but for now, I'm chasing more power. BTW-- did you find the Rels very "picky" in terms of location? Can't wait to hear what the KT150's do in my system.  I/m also contemplating sending my long speaker cables to Audio Art for cutting in half and upgrading to SC-5 SE level and moving the components into another room. This'll also free up bookshelf space for more CDs!  213runnin-- I hear what you're saying about the "last 5%" ... it's wise to recognize that accepting what we've got is often more supportive of peace of mind that obsessive consumerism. Kudos to you!