I see what you mean by listening to your quintet which I like as music, but the samples dont do it justice at all. What are they? They sound like some kind of Microsoft general midi sounds preinstalled in windows (?) and without any effort to manipulate them a little with control messages etc.
I dont know what you use, sequencer or score writer?
I use the score writer side of things cause I always like to write and notate the music fully with every performing nuance irrespective of whether or not the software can play it. Is there a pdf or XML file of this quintet by the way?
I myself use for years the Sibelius score writer (version 8.6 now) which is very expensive for what it offers in my opinion, but at least I'm very pleased in the notational side of things, video and mp3 extraction, etc. but I was never much impressed with its sound library which is massive, slow and not very flexible in terms of midi programming, but a few months ago a friend presented me with an application called Note Performer and since then everything changed to the better. I think it is quite affordable (about 130 euros), but it works presently as a sound engine only with Sibelius. What it does is that it has the ability to read ahead of the score and interpret most markings, so in terms of dynamics, hairpins, crescendo/diminuendo, bowing markings, etc it works fine. I found that their solo and ensemble string samples are quite advanced already (for their price), but they still have to improve on woodwind and brass instruments.
Perhaps you should consider making a change of set up. There is no need to buy Sibelius if you find it too expensive (650-700 dollars as a first time user) and go for Note Performer. Check out MuseScore, which is completely free. It definitely has better sound samples than the ones you use on your quintet, and of course you can further process them with a free DAW like Audacity for better results. There are some collections like Vienna Symphonic Library which can fool (in some pre-programmed pieces only), the most attentive listener that the music is played by human performers, but on one hand they cost over 10000 euros, and on the other the learning curve is so slow and steep, that I consider it the province of a sound engineer and not a creative artist like poet or composer. But have a listen to some of the classic standards there, anyway.