I agree with others in this thread that stated this is a complex question and that sound quality, especially staging, imaging, and timbre (most important to me) is affected by system component synergy more so than an individual component. To me, upgrading a system is a process. I will outline the process I use.
- Establish your perception of the sound of live, acoustic musical performances, both large venue orchestral compositions and small venue chamber music, ensemble jazz, and rock). Large venue rock and jazz is not a good benchmark due to the engineering challenges faced in large venues and variability in sound quality at different seating positions. Note instrument timbre, imaging, image density, staging, macro and micro dynamics, and how the sound blooms from leading edge to harmonic decay.
- Listen to well recorded music, comparing your perception of how live acoustic music sounds and noting differences you which to focus on for improvements.
- Research trade journals for equipment in you budget where the author publishes the equipment excels in sound quality attribute you have identified as an opportunity for improvement.
- Find a good dealer that will let you do an in-store head to head evaluation or better, an in home evaluation, and with a good return policy (with or without a restocking fee. Validate the published review and determine if there is a high benefit/cost ratio.
Responding directly to your question, changing your digital front end can make an improvement in staging and imaging, but you need to be more specific in defining the improvement you wish to make. The attributes of staging include, without limitation; width, depth, presentation (forward or back stage) image focus, image size, image density, ambient bloom in the spaces between performers, ambient bloom into the venue. I will give you my impressions of some DACs you are considering. Remember, my impressions are based on my perception and my ears, so it is a subjective opinion. Your current Innuos DAC has exceptional staging and width, and good focus at its price point. Is presents a more backstage presentation that is light in density and airy. The DCS Lina will be an improvement in all sound quality attributes but will still be a further back presentation, light in density and airy. It will reproduce excellent between instrument and hall ambience and harmonic decay. The MSB is my favorite of the three that will have a up front presentation with dense and palpable images, as well as the between instrument and hall ambience. Others to consider include the Mola Mola Tambaqui, which to my ears is the timbre, dynamics, and soundstage champ, except for between instrument ambience retrieval where the DCS and MSB are better. The MM has an up front presentation (not to the liking of some but to my preference) with excellent width, depth, and focus. The ARC DAC9 excels at bloom (best of the bunch), ambient information retrieval, palpable image density, and stage width and depth. Each of these exceptional products have a distinctive sound pallet, so you need to read information on them and audition to determine which you like. The Nagra is pricy but also an exceptional DAC for the same reasons noted for the ARC.
Improving your amplification will also help. Others have mentioned ARC and CJ tube designs, and Burmester (which I personally do not find dry but rather sweet and highly musical). Others to consider Audio Note (my favorite but above my means) and Gamut. All have their own sound pallet so in repeating myself, research, audition, and choose what brings you emotionally closer to the musical composition and performance. The only right or wrong is determined by your own ears. Good luck.